Obstentrics_Williams

Obstentrics_Williams. Hypervolemia along with decreased vascular resistance has an impressive efect on cardiac function. In one study of 119 women with a twin pregnancy, cardiac output rose another 20 percent above that in women with a singleton pregnancy (Kametas, 2003). Similarly, Kuleva and coworkers (201l) using serial echocardiography found a greater increase in cardiac output in 20 women with uncomplicated twin pregnancies. Both studies found the augmented cardiac output was predominantly due to greater stroke volume rather than higher heart rate. Vascular resistance was signiicantly lower in twin gestations throughout pregnancy compared with singleton ones. In a study of 30 uncomplicated twin pregnancies, this same group of investigators using echocardiography later identified progressive diastolic dysfunction from the irst to third trimester. The dysfunction subsequently normalized after delivery (Ghi, 2015).


Obstentrics_Williams

Obstentrics_Williams. Uterine growth in a multifetal gestation is substantively greater than in a singleton pregnancy. The uterus and its nonfetal contents may achieve a volume of 10 L or more and weigh in excess of 20 pounds. Especially with monozygotic twins, excessive amounts of amnionic luid may rapidly accumulate. In these circumstances, maternal abdominal viscera and lungs can be appreciably compressed and displaced by the expanding uterus. As a result, the size and weight of the large uterus may preclude more than a sedentary existence for these women.


Obstentrics_Williams

Obstentrics_Williams. Ifhydramnios develops, maternal renal function can become seriously impaired, most likely as the consequence of obstructive uropathy (Quigley, 1977). With severe hydramnios, therapeutic amniocentesis may provide relief for the mother, may improve obstructive uropathy, and possibly may lower the preterm delivery risk that follows preterm labor or prematurely ruptured membranes. Unfortunately, hydramnios is often characterized by acute onset remote from term and by rapid reaccumulation despite amniocentesis. Miscarriage is more likely with multifetal gestation. In one 16-year study, the spontaneous abortion rate per live birth in singleton pregnancies was 0.9 percent compared with 7.3 percent in multifetal ones (Joo, 2012). Also, twins achieved through ART are at greater risk for abortion compared with those conceived spontaneously (Szymusik, 2012).


Obstentrics_Williams

Obstentrics_Williams. In some cases, one fetus may be spontaneously lost rather than the entire gestation. As a result, the incidence of twins in the irst trimester is much greater than the incidence of twins at birth. It has been estimated that 1 in 80 births are multifetal, whereas 1 in 8 pregnancies begin multifetal but are spontane ously reduced (Corsello, 2010). Sonography studies in the first trimester have shown that one twin is spontaneously reduced or "vanishes" before the second trimester in up to 10 to 40 percent of all twin pregnancies (Brady, 20l3). The incidence is higher following ART conception. Also, monochorionic twins have a significantly greater risk of spontaneous reduction than dicho rionic twins (Sperling, 2006). Undoubtedly, some threatened abortions are the result of death and resorption of one embryo from an unrecognized twin gestation.


Obstentrics_Williams

Obstentrics_Williams. tion in 709 multifetal pregnancies. Before 12 weeks, one or more embryos died in 36 percent of twin pregnancies, in 53 percent of triplet pregnancies, and in 65 percent of quadru plet pregnancies. Interestingly, ultimate pregnancy duration and birthweight were inversely related to the initial gestational sac number regardless of the final number of fetuses at deliv ery. This efect was most pronounced in twins who started as quadruplets. Chasen and coworkers (2006) reported that spon taneous reduction of an IVF twin pregnancy to a singleton pregnancy was associated with perinatal outcomes intermediate did not undergo spontaneous reduction. Evidence for adverse immediate and long-term efects of twin spontaneous reduction on the remaining pregnancy is conflicting (MeN amara, 2016).


Obstentrics_Williams

Obstentrics_Williams. Notably, spontaneous reduction of a twin gestation may afect prenatal screening results. In one study of ART-conceived gestations, Gjerris and colleagues (2009) compared 56 twin pregnancies with a single early demise and 897 singleton gestations. They found no diferences in irst-trimester serum marker concentrations as long as the embryonic loss was identiied before 9 weeks' gestation. If diagnosed ater 9 weeks, the serum markers were higher and less precise in gestations with an early demise of one twin than in the singleton gestations. With a vanishing twin, first-trimester maternal serum levels of the pregnancy associated plasma protein-A (PAPP-A) can be elevated. Second-trimester MSAFP and dimeric inhibin A levels can also be higher (Huang, 2015). his phenomenon may also afect noninvasive prenatal testing using cell-free DNA (cDNA). In one report, this efect was thought to be responsible for 15 percent of the false-positive results from quantitative counting methods (Futch, 20l3).


Obstentrics_Williams

Obstentrics_Williams. prenatal testing using cell-free DNA (cDNA). In one report, this efect was thought to be responsible for 15 percent of the false-positive results from quantitative counting methods (Futch, 20l3). The recent development of single nucleotide polymorphism technology for cDNA testing appears to hold promise in better identiYing these cases (Curnow, 2015). Regardless, the diagnosis of a spontaneously reduced abortus is ideally excluded to help avoid confusion with results from aneuploidy and neural-tube defect screening.


Obstentrics_Williams

Obstentrics_Williams. As noted earlier, the incidence of congenital malformations is appreciably higher in multifetal gestations compared with that in singleton pregnancies. In one survey-based study, the congenital malformation rate was 406 per 10,000 twins compared with 238 per 10,000 singletons (Glinianaia, 2008). The malformation rate in monochorionic twins was almost twice that of dichorionic twin gestations. This increase has been attributed to the higher incidence of structural defects in monozygotic twins. Indeed, one large population-based study between 1998 and 2010 found that twins had a 73-percent greater risk of congenital heart disease than singletons. The risk was substantially higher among monochorionic twins (Best, 2015). But, from a 30-year European registry of multifetal births, structural anomaly rates rose steadily from 2.16 percent in 1987 to 3.26 percent in 2007 (Boyle, 2013). Yet, during this time, the proportion of dizygotic twins grew by 30 percent, whereas the proportion of


Obstentrics_Williams

Obstentrics_Williams. anomaly rates rose steadily from 2.16 percent in 1987 to 3.26 percent in 2007 (Boyle, 2013). Yet, during this time, the proportion of dizygotic twins grew by 30 percent, whereas the proportion of monozygotic twins remained stable. his higher risk of congenital malformations in dizygotic twins over time correlated with increased availability of AR. An increase in rates of birth defects related to ART has been reported repeatedly (Boulet, 2016; Talauliker, 2012).


Obstentrics_Williams

Obstentrics_Williams. Multifetal gestations are more likely to be low birthweight than singleton pregnancies due to restricted fetal growth and preterm delivery. From 1988 to 2012 at Parkland Hospital, data were collected from 357,205 singleton neonates without malformations and from 3714 normal twins who were both liveborn. Birthweights in twins closely paralleled those of singletons until 28 to 30 weeks' gestation. Thereafter, twin birthweights progressively lagged (Fig. 45-8). Beginning at 35 to 36 weeks' gestation, twin birthweights clearly diverge from those of singletons.


Obstentrics_Williams

Obstentrics_Williams. In general, the degree of growth restriction increases with fetal number. The caveat is that this assessment is based on growth curves established for singletons. Several authorities argue that fetal growth in twins is diferent from that of singleton pregnancies. And thus, abnormal growth should be diagnosed only when fetal size is less than expected for multietal gestation. Accordingly, twin and triplet growth curves have been developed (Kim, 2010; Odibo, 2013; Vora, 2006). At Parkland, we use the standards of birthweight in twin gestations stratified by placental chorionicity for identification of suspected fetal-growth restriction (Ananth, 1998). FIGURE 45-8 Birthweight percentiles (25th to 75th) for 357,205 singleton neonates compared with the 50th birthweight percentile for 3714 twins, Parkland Hospital 1988-2012. Infants with major


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-8 Birthweight percentiles (25th to 75th) for 357,205 singleton neonates compared with the 50th birthweight percentile for 3714 twins, Parkland Hospital 1988-2012. Infants with major FIGURE 45-9 Marked growth discordance in monochorionic twins. (Used with permission from Dr. Laura Greer.) he degree of growth restriction in monozygotic twins is likely to be greater than that in dizygotic pairs (Fig. 45-9). With monochorionic embryos, allocation of blastomeres may not be equal, vascular anastomoses within the placenta may cause unequal distribution of nutrients and oxygen, and discordant structural anomalies resulting from the twinning event itself may afect growth. For example, the quintuplets shown in Figure 45-10 represent three dizygotic and two monozygotic fetuses. When delivered at 31 weeks, the three neonates from separate ova weighed 1420, 1530, and 1440 g, whereas the two derived from the same ovum weighed 990 and 860 g.


Obstentrics_Williams

Obstentrics_Williams. In the third trimester, the larger fetal mass leads to accelerated placental maturation and relative placental insuiciency. In dizygotic pregnancies, marked size discordancy usually results from unequal placentation, with one placental site receiving more perfusion than the other. Size diferences may also reflect diferent genetic fetal-growth potentials. Discordancy can also result from fetal malformations, genetic syndromes, infection, or umbilical cord abnormalities such as velamentous insertion ' marginal insertion, or vasa previa (Chap. 44, p. 849).


Obstentrics_Williams

Obstentrics_Williams. Pregnancy-related hypertensive disorders are more likely to develop with multifetal gestations. The exact incidence attributable to twin pregnancy is diicult to determine because these gestations are more likely to deliver preterm and before preeclampsia usually develops. Also, women with twin pregnancies are often older and multiparous, qualities associated with lower rates of preeclampsia (Francisco, 2017). The incidence of pregnancy-related hypertension in women with twins is 20 percent at Parkland Hospital. In their analysis of 513 twin malformations, pregnancies complicated by stillbirth, and twin gestations with >25 percent discordance were also excluded. (Data from Dr. Don Mcintire.) pregnancies, Fox and coworkers (2014) identified 15 percent of parturients with preeclampsia. Another study compared 257 women with twins and gestational diabetes against 277 nondiabetic women carrying twins. hese researchers found a twofold greater risk of preeclampsia in women diagnosed with


Obstentrics_Williams

Obstentrics_Williams. study compared 257 women with twins and gestational diabetes against 277 nondiabetic women carrying twins. hese researchers found a twofold greater risk of preeclampsia in women diagnosed with gestational diabetes (Gonzalez, 2012). Conversely, no specific zygosity confers a greater rate of hypertensive disorder in twin pregnancies (Lucovnik, 2016). Finally, from the National Center for Health Statistics, Luke and associates (2008) analyzed 316,696 twin, 12,193 triplet, and 778 quadruplet pregnancies. hese investigators noted that the risk for pregnancy-associated hypertension was significantly increased for triplets and quadruplets (11 and 12 percent, respectively) compared with that for twins (8 percent).


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-10 Davis quintuplets at 3 weeks following delivery. The first, second, and fourth newborns from the left each arose from separate ova, whereas the third and fifth neonates are from the same ovum.


Obstentrics_Williams

Obstentrics_Williams. hese data suggest that fetal number and placental mass are involved in preeclampsia pathogenesis. Women with twin pregnancies have levels of antiangiogenic soluble fms-like tyrosine kinase-1 (sFlt-1) that are twice that of singletons. Levels are seemingly related to greater placental mass rather than primary placental pathology (Bdolah, 2008; Maynard, 2008). Rana and coworkers (2012) measured antiangiogenic sFlt-1 and proangiogenic placental growth factor (PIGF) in 79 women with twins referred for evaluation of preeclampsia. In the 58 women identiied with either gestational hypertension or preeclampsia, there was an incremental rise in sFlt-1 concentrations, decline in PIGF levels, and increase in sFlt-lIPIGF ratios compared with normotensive twin pregnancies. With multifetal gestation, hypertension not only develops more often but also tends to develop earlier and be more severe. In the analysis of angiogenic factors mentioned above, more than half of afected women presented before


Obstentrics_Williams

Obstentrics_Williams. hypertension not only develops more often but also tends to develop earlier and be more severe. In the analysis of angiogenic factors mentioned above, more than half of afected women presented before 34 weeks, and their sFlt-lIPIGF ratio rise was more striking (Rana, 2012). This relationship is discussed in Chapter 40 (p. 716).


Obstentrics_Williams

Obstentrics_Williams. The duration of gestation shortens with accruing fetal number. More than five of every 10 twins and nine of 10 triplets born in the United States in 2015 were delivered preterm (Martin, 2017). Prematurity is sixfold and tenfold greater in twins and triplets, respectively (Giufre, 2012). One review showed that approximately 60 percent of preterm births in twins are indicated, about a third result from spontaneous labor, and 10 percent follow prematurely ruptured membranes (Chauhan, 2010). In another analysis of almost 300,000 live births, the proportion of preterm birth associated with premature membrane rupture rose with gestational plurality from 13 percent with singletons to 20 percent with triplets or more (Pakrashi, 2013).


Obstentrics_Williams

Obstentrics_Williams. Although the causes of preterm delivery in twins and singletons may be diferent, neonatal outcome is generally the same at similar gestational ages (Kilpatrick, 1996; Ray, 2009; Salem, 2017). However, outcomes for pre term twins who are markedly discordant may not be comparable with those for singletons because whatever caused the discordance may have long-lasting efects (Yinon, 2005) . Historically, twins have been considered cognitively delayed compared with singletons (Record, 1970; Ronalds, 2005). However, in cohort studies evaluating normal-birthweight term newborns, cognitive outcomes between twins and singletons are similar (Lorenz, 2012). Christensen and associates (2006) found similar national standardized test scores in the ninth grade in 341r1 twins and 7796 singletons born between 1986 and 1988.


Obstentrics_Williams

Obstentrics_Williams. In contrast, among normal-birthweight neonates, the cerebral palsy risk is higher among twins and higher-order multiples. For example, the cerebral palsy rate has been reported to be 2.3 per 1000 in singletons, 12.6 per 1000 in twins, and 44.8 per 1000 in triplets (Giufre, 2012). Greater risks of fetalgrowth restriction, congenital anomalies, twin-twin transfusion syndrome, and fetal demise of a cotwin are suggested contributors to these diferences (Lorenz, 2012). Several unique complications arise in multifetal pregnancies. These are described in twins but can be found in higher-order multifetal gestations. Most fetal complications due to the twinning process itself are seen with monozygotic twins. heir pathogenesis is best understood after reviewing the possibilities shown in Figure 45-1.


Obstentrics_Williams

Obstentrics_Williams. Only about 1 percent of all monozygotic twin gestations will share an amnionic sac, and approximately 1 in 20 monochorionic twin gestations are monoamnionic (Hall, 2003; Lewi, 2013). Diamnionic twins can become monoamnionic if the dividing membrane spontaneous or iatrogenically ruptures. Their morbidity and mortality rates then mirror those of monoamnionic twins.


Obstentrics_Williams

Obstentrics_Williams. Historical mortali ty rates in monoamnionic twins were reported to be as high as 70 percent. Contemporary outcomes are improved, yet the demise rate after viability remains elevated (Post, 2015). Of those fetuses alive before 16 weeks' gestation, less than half survive until the neonatal period. Fetal abnormalities and spontaneous miscarriage contribute to most losses (Prefumo, 2015). After 20 weeks, the perinatal mortality rate for monoamnionic twin pregnancies approximates 15 percent (Shub, 2015). A high fetal death rate is attributable to preterm birth, congenital anomalies, twin-twin transfusion syndrome, or cord entanglement.


Obstentrics_Williams

Obstentrics_Williams. Congenital anomaly rates in monoamnionic twins reach 18 to 28 percent (Post, 2015). Since concordance of anomalies is found in only approximately one quarter of cases, the finding of normal anatomy in one twin does not negate the need for a thorough evaluation in the second. Also, because of the higher risk of cardiac anomalies, fetal echo cardiography is indicated in these pregnancies. Of note, monoamnionic twins are by definition monozygotic and thus presumed to be genetically identical. Consequently, either both or none of the fetuses have chromosomal abnormalities except in rare cases of discordance (Zwijnenburg, 2010). Indeed, the risk for Down syndrome in each fetus of the monozygotic pair is similar to or lower than the risk in maternal age-matched singletons (Sparks, 2016). he standard methods for Down syndrome screening in these pregnancies can be applied (Chap. 14, p. 281).


Obstentrics_Williams

Obstentrics_Williams. The rate of twin-twin transfusion syndrome in monoamnionic twins is lower than the rate reported in monochorionic diamnionic pregnancies. This may be due to the near universal presence in monoamnionic twins of arterioarterial anastomoses, which are presumed to be protective (Hack, 2009b; Post, 2015). Nonetheless, twin-twin transfusion syndrome surveillance is recommended and described on page 879. Umbilical cords frequently entangle (Fig.


Obstentrics_Williams

Obstentrics_Williams. Umbilical cords frequently entangle (Fig. lorbid cord entanglement appears to occur early, and monoamnionic pregnancies that have successfully reached 30 to 32 weeks' gestation are at reduced risk. In one Dutch series, the incidence of intrauterine demise dropped from 15 percent after 20 weeks to 4 percent at gestational ages >32 weeks (Hack, 2009a). Although color-low Doppler sonography is used to diagnose entanglement (Fig. 45-12), factors that lead to pathological umbilical vessel constnctton are unknown. A consequence is that fetal death from cord entanglement is unpredictable. Unfortunately, monitoring for this is relatively inefective. In one study, after analysis of more than 10,000 hours of fetal tracing from 17 sets of monoamnionic twins, Quinn and colleagues (2011) concluded that monitoring was physically FIGURE 45-1 1 Monozygotic twins in a single amnionic sac. The smaller fetus apparently died first, and the second subsequently succumbed when umbilical cords entwined.


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-1 1 Monozygotic twins in a single amnionic sac. The smaller fetus apparently died first, and the second subsequently succumbed when umbilical cords entwined. FIGURE 45-12 Monochorionic monoamnionic cord entanglement. A. Despite marked knotting of the cords, vigorous twins were delivered by cesarean. B. Preoperative sonogram of this pregnancy shows entwined cords. C. This finding is accentuated with application of color Doppler. (Used with permission from Dr. Julie Lo.) FIGURE 45-13 Possible outcomes of monozygotic twinning. The asymmetrical category contains twinning types in which one twin complement is substantially smaller and incompletely formed. possible in only 50 percent of cases. An abnormal fetal heart rate tracing prompted delivery in only six cases.


Obstentrics_Williams

Obstentrics_Williams. One proposed management scheme is based on a study by Heyborne and coworkers (2005), who reported no stillbirths in 43 twin pregnancies of women admitted at 26 to 27 weeks' gestation for daily fetal surveillance. However, in 44 women managed as outpatients and admitted only for obstetrical indications, there were 13 stillbirths. Because of this report, women with monoamnionic twins are recommended to undergo 1 hour of daily fetal heart rate monitoring, either as an outpatient or inpatient, beginning at 26 to 28 weeks' gestation. With initial testing, a course of betamethasone is given to promote pulmonary maturation (Chap. 42, p. 823). If fetal testing remains reassuring and no other intervening indications arise, cesarean delivery is performed at 32 to 34 weeks. A second course of betamethasone can be given before this (American College of Obstetricians and Gynecologists, 2016). his management scheme is used at Parkland Hospital and resulted in the successful 34-week delivery of the


Obstentrics_Williams

Obstentrics_Williams. can be given before this (American College of Obstetricians and Gynecologists, 2016). his management scheme is used at Parkland Hospital and resulted in the successful 34-week delivery of the twins depicted in Figure 45-12.


Obstentrics_Williams

Obstentrics_Williams. Of monoamnionic twins just described, one interesting subset derives from embryonic splitting on postfertilization day 9. These "mirror image twins" are genetically identical but have mirror image features such as handedness and hair whorls (Post, 2015). More seriously, several aberrations in monozygotic twinning result in a spectrum of fetal malformations. hese are traditionally ascribed to incomplete splitting of an embryo into two separate twins. However, it is possible that they may result from early secondary fusion of two separate embryos. These separated embryos are either symmetrical or asymmetrical, and the spectrum of anomalies is shown in Figure 45-13.


Obstentrics_Williams

Obstentrics_Williams. In the United States, united or conjoined twins have been referred to as Siamese twins-after Chang and Eng Bunker of Siam (Thailand), who were displayed worldwide by P. T. Barnum. Joining of the twins may begin at either pole and produce characteristic forms depending on which body parts are joined or shared (Fig. 45-14). Of these, thoracopagus is the most common (Mutchinick, 2011). he frequency of conjoined twins is not well established. In Singapore, Tan and coworkers (1971) identified seven cases of conjoined twins among more than 400,000 deliveries-an incidence of 1 in 60,000.


Obstentrics_Williams

Obstentrics_Williams. Conjoined twins can frequently be identiied using sonography at midpregnancy (McHugh, 2006). his provides an opportunity for parents to decide whether to continue the pregnancy. As shown in Figure 45-15, identification of cases during the first trimester is also possible. During sonographic interrogation, fetal poles are closely associated and do not change relative position from one another. A targeted examination, including a careful evaluation of the organs involved, is necessary before counseling can be provided. As shown in Figure 45-16, MR imaging is a valuable adjunct to clariY shared organs. Compared with sonography, MR imaging can provide superior views, especially in later pregnancy when amnionic luid is diminished and fetal crowding is greater (Hibbeln, 2012).


Obstentrics_Williams

Obstentrics_Williams. Surgical separation of an almost completely joined twin pair may be successful if essential organs are not shared (O'Brien, 2015; Tannuri, 20l3). Conjoined twins may have discordant structural anomalies that further complicate decisions about whether to continue the pregnancy. Consultation with a pediatric surgeon often assists parental decision making. A recent FIGURE 45-14 Types of conjoined twins. (Modified with permission from Spencer R: Theoretical and analytical embryology of conjoined . Parapagus Parapagus twins: part I: embryogenesis, (lin Anat. 2000;13(1 ):36-53.) series in Seminars in Pediatric Surgey with a preface by Spitz (2015) provide an excellent reference regarding postnatal management.


Obstentrics_Williams

Obstentrics_Williams. Viable conjoined twins should be delivered by cesarean. For the purpose of pregnancy termination, however, vaginal delivery is possible because the union is most often pliable (Fig. 45-17). Still, dystocia is common, and if the fetuses are mature, vaginal delivery may be traumatic to the uterus or cervix. his is a grossly defective fetus or merely fetal parts, attached externally to a relatively normal twin. A parasitic twin usually consists of externally attached supernumerary limbs, often with some viscera. Classically, however, a functional heart or brain is absent. Attachment mirrors those sites described earlier for conjoined twins (see Fig. 45-14). Parasites are believed to result from demise of the defective twin. Its surviving tissue attaches to and receives vascularity from the normal cotwin (Spencer, 2001). In one large epidemiological study, parasitic twins accounted for 4 percent of all conjoined twins and occurred more frequently in male fetuses (Mutchinick, 2011).


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-15 Sonogram of a conjoined twin pregnancy at 13 weeks' gestation. These thoracoomphalopagus twins have two heads but a shared chest and abdomen. Early in development, one embryo may be enfolded within its twin. Normal development of this rare parasitic twin usually arrests in the first trimester. As a result, norml spatial arrangement of and presence of many organs is lost. Classically, vertebral or xial bones are found in the fetiform mass, whereas a heart and brain are absent. hese masses are believed to represent a monozygotic, monochorionic diamnionic twin gestation and are typically supported by large parasitic vessels to the host (McNamara, 2016; Spencer, 2000). Malignant degeneration is rare (Kaufman, 2007). All monochorionic placentas likely share some anastomotic connections. And, with rare exceptions, anastomoses between


Obstentrics_Williams

Obstentrics_Williams. All monochorionic placentas likely share some anastomotic connections. And, with rare exceptions, anastomoses between FIGURE 45-16 Magnetic resonance imaging of conjoined twins. This T2-weighted HASTE sagittal image demonstrates fusion from the level of the xiphoid process to just below the level of the umbilicus, that is, omphalopagus twins. Below the fused liver (L)/ there is a midline cystic mass (arrow) within the tissue connecting the twins. An omphalomesenteric cyst was favored given the location within the shared tissue. (Used with permission from Dr. April Bailey.)


Obstentrics_Williams

Obstentrics_Williams. Dr. April Bailey.) FIGURE 45-17 Conjoined twins aborted at 17 weeks' gestation. (Used with permission from Dr. Jonathan Willms.) twins are unique to monochorionic twin placentas. However, the number, size, and direction of these seemingly haphazard connections vary markedly (Fig. 45-18). In one analysis of more than 200 monochorionic placentas, the median number of anastomoses was 8, with an interquartile range of 4 to 14 (Zhao, 2013).


Obstentrics_Williams

Obstentrics_Williams. Artery-to-artery anastomoses are most frequent and are identiied on the chorionic surface of the placenta in up to 75 percent of monochorionic twin placentas. Vein-to-vein and artery-to-vein communications are each found in approximately half. One vessel may have several connections, sometimes to both arteries and veins. In contrast to these supericial vascular connections on the surface of the chorion, deep arteryto-vein communications can extend through the capillary bed of a given villus (Fig. 45-19). hese deep arteriovenous anastomoses create a common villous compartment or "third circulation" that has been identiied in approximately half of monochorionic twin placentas.


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-19 Anastomoses between twins may be artery-tovein (AV), artery-to-artery (AA), or vein-to-vein (W). Schematic representation of an AV anastomosis in twin-twin transfusion syndrome that forms a "common villous district" or "third circulation" deep within the villous tissue. Blood from a donor twin may be transferred to a recipient twin through this shared circulation. This transfer leads to a growth-restricted discordant donor twin with markedly reduced amnionic fluid, causing it to be "stuck." Whether these anastomoses are dangerous to either twin depends on the degree to which they are hemodynamically balanced. In those with signiicant pressure or low gradients, a shunt will develop between fetuses. his chronic fetofetal transfusion may result in several clinical syndromes that include


Obstentrics_Williams

Obstentrics_Williams. FIGURE 45-18 Shared placenta from pregnancy complicated by twin-twin transfusion syndrome. The following color code was applied for injection. Left twin: yellow = artery, blue = vein; right twin: red = artery, green = vein. A. Part of the arterial network of the right twin is filled with yellow dye, due to the presence of a small artery-to-artery anastomosis (arrow). B. Close-up of the lower portion of the placenta displays the yellow dye-filled anastomosis. (Reproduced with permission from De Paepe ME, DeKoninck P, Friedman RM: Vascular distribution patterns inmonochorionic twin placentas, Placenta. 2005 Jul;26(6):471-475.) FIGURE 45-20 These serial sonograms depict an interventricular hemorrhage with parenchymal extension and eventual porencephaly that developed following cotwin demise in a monochorionic pregnancy. From left to right, these images were obtained 1 week,o5 weeks, and 8 weeks following demise of the cotwin.


Obstentrics_Williams

Obstentrics_Williams. twin-twin transfusion syndrome (TTTS), twin anemia poycythemia sequence (TAPS), and acardiac twinning. In this syndrome, blood is transfused from a donor twin to its recipient sibling such that the donor may eventually become anemic and its growth may be restricted. In contrast, the recipient becomes polycythemic and may develop circulatory overload manifest as hydrops. Classically, the donor twin is pale, and its recipient sibling is plethoric. Similarly, one portion of the placenta often appears pale compared with the remainder. The recipient neonate may also have circulatory overload from heart failure and severe hypervolemia and hyperviscosity. Occlusive thrombosis is another concern. Finally, polycythemia in the recipient twin may lead to severe hyperbilirubinemia and kernicterus (Chap. 33, p. 626). he prevalence of TTTS approximates 1 to 3 cases per 10,000 births (Society for Maternal-Fetal Medicine, 2013).


Obstentrics_Williams

Obstentrics_Williams. Chronic TTTS results from unidirectional low through deep arteriovenous anastomoses. Deoxygenated blood from a donor placental artery is pumped into a cotyledon shared by the recipient (see Fig. 45-19). Once oxygen exchange is completed in the chorionic villus, the oxygenated blood leaves the cotyledon via a placental vein of the recipient twin. Unless compensatedtypically through superficial arterioarterial anastomoses-this unidirectional low leads to an imbalance in blood volumes (Lewi, 2013). Clinically important TTTS frequently is chronic and results from significant vascular volume diferences between the twins. Even so, the pathogenesis is more complex than a net transfer of red blood cells from one twin to another. Indeed, in most monochorionic twin pregnancies with the syndrome, hemoglobin concentrations between the donor and recipient twin do not difer (Lewi, 2013).


Obstentrics_Williams

Obstentrics_Williams. TTTS typically presents in midpregnancy when the donor fetus becomes oliguric from decreased renal perfusion (Society for Maternal-Fetal Medicine, 2013). This fetus develops oligohydramnios, and the recipient fetus develops severe hydramnios, presumably due to increased urine production. Virtual absence of amnionic fluid in the donor sac prevents fetal motion, giving rise to the descriptive term stuck twin or poyhydramnios-oligohydramnios syndrome-'poy-oli. " This amnionic fluid imbalance is associated with growth restriction, contractures, and pulmonary hypoplasia in the donor twin, and premature rupture of the membranes and heart failure in the recipient.


Obstentrics_Williams

Obstentrics_Williams. Fetal Brain Damage. Cerebral palsy, microcephaly, porencephaly, and multicystic encephalomalacia are serious complications associated with placental vascular anastomoses in multifetal gestation. he exact pathogenesis of neurological damage is not fully understood but is likely caused by ischemic necrosis leading to cavitary brain lesions (Fig. 45-20). In the donor twin, ischemia results from hypotension, anemia, or both. In the recipient, ischemia develops from blood pressure instability and episodes of profound hypotension (Lopriore, 2011). Cerebral lesions may also be due to postnatal injury associated with preterm delivery (Chap. 34, p. 639). In one review of315 liveborn fetuses from pregnancies with TTTS, cerebral abnormalities were found in 8 percent (Quarello, 2007).


Obstentrics_Williams

Obstentrics_Williams. If one twin of an afected pregnancy dies, cerebrl pathology in the survivor probably results from acute hypotension. A less likely cause is emboli of thromboplastic material originating from the dead fetus. Fusi and coworkers (1990, 1991) observed that with the death of one twin, acute twin-twin anastomotic transusion from the high-pressure vessels of the living twin to the lowresistance vessels of the dead twin leads rapidly to hypovolemia and ischemic antenatal brain damage in the survivor. In one review of 343 twin pregnancies complicated by single fetal demise, the risk of neurodevelopmental morbidity in monochorionic twins was 26 percent compared with 2 percent in dichorionic twins (Hillman, 2011). This morbidity was related to the gestational age at the death of the cotwin. If the death occurred between 28 and 33 weeks' gestation, monochorionic twins had an almost eightfold risk of neurodevelopmental morbidity compared with dichorionic twins of the same gestational age. With


Obstentrics_Williams

Obstentrics_Williams. death occurred between 28 and 33 weeks' gestation, monochorionic twins had an almost eightfold risk of neurodevelopmental morbidity compared with dichorionic twins of the same gestational age. With fetal death ater 34 weeks, the likelihood dramaticlly decreased-odds ratio 1.48.


Obstentrics_Williams

Obstentrics_Williams. he acuity of hypotension following the death of one twin with TTTS makes successful intervention for the survivor nearly impossible. Even with delivery immediately ater a cotwin demise is recognized, the hypotension that occurs at the moment of death has likely already caused irreversible brain damage (Langer, 1997; Wada, 1998). s such, immediate delivery is not considered beneficial in the absence of another indication.


Obstentrics_Williams

Obstentrics_Williams. Diagnosis. he criteria used to diagnose and classiy varying severities of TTTS have dramatically changed. Previously, weight discordancy and hemoglobin diferences in monochorionic twins were calculated. However, in many cases, these are late findings. According to the Society for Maternal-Fetal Medicine (2013), TTTS is diagnosed based on two so nographic criteria. First, a monochorionic diamnionic pregnancy is identified. Second, hydramnios defined by a largest vertical pocket > 8 em in one sac and oligohydramnios defined by a largest vertical pocket <2 em in the other twin is found. Only 15 percent of pregnancies complicated by lesser degrees of luid imbalance progress to TTTS (Huber, 2006). Although growth discordance or growth restriction may be found with TTTS, these per se are not considered diagnostic criteria.


Obstentrics_Williams

Obstentrics_Williams. Organizations that include the American College of Obstetricians and Gynecologists (2016), Society for Maternal-Fetal Medicine (2013), and North American Fetal herapy Network (Emery, 2015) recommend sonography surveillance of pregnancies at risk for TTTS. To aid earlier identification of amnionic luid abnormalities and other complications of monochorionic twins, these examinations begin at approximately 16 weeks' gestation, and subsequent studies are considered every 2 weeks. Once identiied, TTTS is typically classiied by the Quintero (1999) staging system (Fig. 45-21): Stage I-discordant amnionic fluid volumes as described in the earlier paragraph, but urine is still visible sonographically within the bladder of the donor twin Stage II-criteria of stage I, but urine is not visible within the donor bladder Stage III-criteria of stage II and abnormal Doppler studies of the umbilical artery, ductus venosus, or umbilical vein Stage V-demise of either fetus.


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Obstentrics_Williams. Stage III-criteria of stage II and abnormal Doppler studies of the umbilical artery, ductus venosus, or umbilical vein Stage V-demise of either fetus. In addition to these criteria, evidence suggests that cardiac function of the recipient twin correlates with fetal outcome (Crombleholme, 2007). Although fetal echocardiographic indings are not part of the Quintero staging system, many centers routinely perform fetal echocardiography for TTTS. heoretically, earlier diagnosis of cardiomyopathy in the recipient twin may identiy pregnancies that would beneit from early intervention. One system for evaluating cardiac function-the myocardial peormance index (MPI) or Tei index-is a Doppler index of ventricular function calculated for each ventricle (Michelfelder, 2007). lthough scoring systems that include assessment of cardiac function have been developed, their usefulness to predict outcomes remains controversial (Society for Maternal-Fetal Medicine, 2013).


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Obstentrics_Williams. Management and Prognosis. he prognosis for mulrifetal gestations complicated by TTTS is related to Quintero stage and gestational age at presentation. More than three fourths of stage I cases have been reported to remain stable or regress without intervention. Conversely, outcomes in those identiied at stage III or higher are much worse, and the perinatal loss rate is 70 to 100 percent without intervention (Society for Maternal-Fetal Medicine, 2013). At Parkland Hospital, among expectantly managed pregnancies with TTTS, most had early disease at diagnosis, and 50 percent of stage I cases progressed (Duryea, 2016).


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Obstentrics_Williams. Several therapies are available for TTTS and include amnioreduction, laser ablation of vascular placental anastomoses, selective feticide, and septosromy. Described further in Chapter 11 (p. 230), amnioreduction describes needle drainage of excess amnionic fluid. Septostomy is intentionally creating a hole in the dividing amnionic membrane but has largely been abandoned as treatment (Society for Maternal-Fetal Medicine, 2013). Comparative data from randomized trials for some of these other techniques are discussed below.


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Obstentrics_Williams. The Eurofetus trial included 142 women with severe TTTS diagnosed before 26 weeks. Participants were randomly assigned to laser ablation of vascular anastomoses or to serial amnioreduction (Senat, 2004). A higher survival rate to age 6 months for at least one twin was found in pregnancies undergoing laser ablation-76 versus 51 percent, respectively. Moreover, analyses of randomized studies confirm better neonatal outcomes with laser therapy compared with selective amnioreduction (Roberts, 2008; Rossi, 2008, 2009). In contrast, Crombleholme and associates (2007), in a randomized trial of 42 women, found equivalent rates of 30-day survival of one or both twins treated with either amnioreduction or selective fetoscopic laser ablation-75 versus 65 percent, respectively. Furthermore, evaluation of twins from the Eurofetus trial through 6 years of age did not demonstrate an additional survival benefit beyond 6 months or improved neurological outcomes in those treated with laser (Salomon,


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Obstentrics_Williams. of twins from the Eurofetus trial through 6 years of age did not demonstrate an additional survival benefit beyond 6 months or improved neurological outcomes in those treated with laser (Salomon, 2010). At this time, laser ablation of anastomoses is preferred for severe TTTS (stages II-IV). Optimal therapy for stage I disease is controversial.


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Obstentrics_Williams. FIGURE 45-21 A. Sonogram of stage I ms at 19 weeks' gestation. Oligohydramnios in the donor twin sac causes the membrane to essentially wrap around the "stuck twin" and suspend it from the anterior uterine wall. B. In this same pregnancy, hydramnios is seen in the recipient twin sac. The measured pocket exceeds 10 cm. C. Stage II ms in a donor twin at 17 weeks' gestation. Color Doppler highlights the arteries that outline the fetal bladder, which contains no urine. After laser therapy, close ongoing surveillance is necessary.


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Obstentrics_Williams. After laser therapy, close ongoing surveillance is necessary. Robyr and colleagues (2006) reported that a fourth of 101 pregnancies treated with laser required additional invasive therapy because of either recurrent TTTS, or middle cerebral artery (MCA) Doppler evidence of anemia or polycythemia. Recently, in a comparison of selective laser ablation of individual anastomoses versus ablation of the entire surface of the chorionic plate along the vascular equator, Baschat and coworkers (2013) found that equatorial photocoagulation reduced the likelihood of recurrence.


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Obstentrics_Williams. Selective fetal reduction has generally been considered if severe amnionic luid and growth disturbances develop before 20 weeks. In such cases, both fetuses typically will die without intervention. Any substance injected into one twin may afect the other twin because of shared circulations. hus, for the fetus chosen for reduction, feticidal techniques include methods that occlude the umbilical vein or umbilical cord of using radiofrequency ablation, fetoscopic ligation, or coagulation with laser, monopolar, or bipolar energy (Challis, 1999; Chang, 2009; Parra-Cordero, 2016). Even after these procedures, however, the risks to the remaining fetus are still appreciable (Rossi, 2009). This topic is further discussed on page 891.


Obstentrics_Williams

Obstentrics_Williams. This form of chronic fetofetal transfusion, referred to as TAPS, is characterized by significant hemoglobin diferences between donor and recipient twins. However, TAPS lacks the discrepancies in amnionic luid volumes typical of TTTS (Slaghekke, 2010). It is diagnosed ante natally by M CA peak systolic velocity (PSV) > 1.5 multiples of the median (MoM) in the donor and < 1.0 MoM in the recipient twin (Society for MaternalFetal Medicine, 2013). The spontaneous form of TAPS reportedly complicates 3 to 5 percent of monochorionic pregnancies, and it occurs in up to 13 percent of pregnancies after laser photocoagulation of the placenta. Spontaneous TAPS usually occurs after 26 weeks' gestation, and iatrogenic TAPS develops within 5 weeks of a procedure (Lewi, 2013). Although a staging system has been proposed by Slaghekke and colleagues (2010), further studies are necessary to better elucidate the natural history of TAPS and its management. In brief, evidence of fetal compromise or greater


Obstentrics_Williams

Obstentrics_Williams. been proposed by Slaghekke and colleagues (2010), further studies are necessary to better elucidate the natural history of TAPS and its management. In brief, evidence of fetal compromise or greater diferences in MCA PSV between twins raise the stage.


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Obstentrics_Williams. lso known as an acardiac twin, this is a rare but serious complication of monochorionic multifetal gestation. n estimated incidence is 1 case in 35,000 births. In the classic twin reversedarterial-perfusion (TRAP) sequence, there is a normally formed donor twin that shows features of heart failure and a recipient twin that lacks a heart (acardius) and other structures. In one theory, the TRAP sequence is caused by a large artery-to-artery placental shunt, often also accompanied by a vein-to-vein shunt


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Obstentrics_Williams. FIGURE 45-22 Twin reversed-arterial-perfusion sequence. In the TRAP sequence, there is usually a normally formed donor twin that has features of heart failure, and a recipient twin that lacks a heart. It has been hypothesized that the TRAP sequence is caused by a large artery-to-artery placental shunt, often also accompanied by a vein-to-vein shunt. Within the single, shared placenta, perfusion pressure of the donor twin overpowers that in the recipient twin, who thus receives reverse blood flow from its twin sibling. The "used" arterial blood that reaches the recipient twin preferentially goes to its iliac vessels and thus perfuses only the lower body. This disrupts growth and development of the upper body.


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Obstentrics_Williams. (Fig. 45-22). Within the single, shared placenta, arterial perfusion pressure of the donor twin exceeds that in the recipient twin, who thus receives reverse blood low containing deoxygenated arterial blood from its cotwin (Lewi, 2013). his "used" arterial blood reaches the recipient twin through its umbilical arteries and preferentially goes to its iliac vessels. Thus, only the lower body is perfused, and therefore disrupted growth and development of the upper body results. In these cases, failed head growth is called acardius acephalus; a partially developed head with identifiable limbs is called acardius myelacephalus; and failure of any recognizable structure to form is acardius amorphous, which is shown in Figure 45-23 (Faye-Petersen, 2006). Because of this vascular connection, the normal donor twin must not only support its own circulation but also pump blood through the underdeveloped acardiac recipient. This may lead to cardiomegaly and high-output heart failure in the normal


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Obstentrics_Williams. donor twin must not only support its own circulation but also pump blood through the underdeveloped acardiac recipient. This may lead to cardiomegaly and high-output heart failure in the normal twin (Fox, 2007).


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Obstentrics_Williams. In the past, the mortality rate among the pump twins exceeded 50 percent. This stemmed largely from complications of prematurity or from a prolonged high-output state leading to cardiac failure (Dashe, 2001). Risk appears to be directly related to size of the acardiac twin. One sonographic method to estimate acardiac twin size uses the volume of an ellipse: length X width X height x \/6. When the acardiac twin volume is < 50 percent of that of the pump twin, expectant management may be reasonable given the inherent risks of fetal intervention (Chap. 15, p. 326)(Jelin, 2010). When the volume of the


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Obstentrics_Williams. FIGURE 45-23 Photograph of an acardiac twin weighing 475 grams. The underdeveloped head is indicated by the black arrow, and its details are shown in the inset. A yellow clamp is seen on its umbilical cord. Its viable donor cotwin was delivered vaginally at 36 weeks and weighed 2325 grams. (Used with permission from Dr. Michael D. Hnat.) acardiac twin is large, however, treatment has generally been ofered. Radiofrequencyrablation (RFA) is the preferred modality of therapy, and contemporary reports now suggest improved perinatal outcomes. he North American Fetal Therapy Network reviewed their experiences with 98 cases from 1998 to 2008 in which RF A of the umbilical cord was performed (Lee, 2013). Median gestational age at delivery was 37 weeks, and 80 percent of neonates survived (Lee, 20l3). he average gestational age at the time of the RF A was 20 weeks, and the estimated acardius-to-pump twin volume on average was 90 percent. Major complications were prematurely ruptured membranes


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Obstentrics_Williams. he average gestational age at the time of the RF A was 20 weeks, and the estimated acardius-to-pump twin volume on average was 90 percent. Major complications were prematurely ruptured membranes and preterm birth.


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Obstentrics_Williams. Interestingly, TRAP sequences can also occur within monoamnionic pregnancies. he perinatal outcomes of such pregnancies appear to be worse than that of monochorionic diamnionic cases. Sugibayashi and associates (2016) in a review of 40 cases recently reported that pump twin survival following RF A was 88 percent in monochorionic diamnionic pregnancies but only 67 percent in monoamnionic pregnancies. • Hydatidiform Mole with Coexisting Normal Fetus his unique gestation contains one normal fetus, and its cotwin is a complete molar pregnancy. Reported prevalence rates range from 1 in 22,000 to 1 in 100,000 pregnancies (Dolapcioglu, 2009). It must be diferentiated from a partial molar pregnancy, in which an anomalous singleton fetususually triploid-is accompanied by molar tissue (Fig. 20-4, p. 391). At times, a twin pregnancy may occur with a normal twin in one sac and a partial mole in the other sac (McN amara, 2016). Diagnosis is usually made in the first half of pregnancy.


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Obstentrics_Williams. Sonographically, a normal-appearing twin is accompanied by its cotwin, which is a large placenta containing multiple small anechoic cysts (Fig. 20-4, p. 391). Often, these pregnancies are terminated, but pregnancy continuation is increasingly adopted. First, the pregnancy prognosis is not as poor as previously thought, and live birth rates range between 20 and 40 percent (Dolapcioglu, 2009; McNamara, 2016). Second, the risk of persistent trophoblastic disease is similar whether the pregnancy is terminated or not (Massardier, 2009; Sebire, 2002). That said, given the limited number of cases, robust data for irm recommendations are lacking. Importantly, complications of expectant management include vaginal bleeding, hyperemesis gravidarum, thyrotoxicosis, and early-onset preeclampsia (McNamara, 2016). Many of these complications result in preterm birth with its attendant adverse perinatal sequelae as well as perinatal loss. Logically, close surveillance is needed for those continuing


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Obstentrics_Williams. 2016). Many of these complications result in preterm birth with its attendant adverse perinatal sequelae as well as perinatal loss. Logically, close surveillance is needed for those continuing the pregnancy.


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Obstentrics_Williams. Fetal size inequality develops in approximately 15 percent of twin gestations and may relect pathological growth restriction in one fetus (Lewi, 2013; Miller, 2012). Generally, as the weight diference within a twin pair rises, the perinatal mortality rate increases proportionately. If it develops, restricted growth of one twin fetus, often termed selective etal-growth restriction, usually develops late in the second and early third trimester. Earlier discordancy indicates higher risk for fetal demise in the smaller twin. Speciically, when discordant growth is identified before 20 weeks, fetal death occurs in approximately 20 percent of the growth-restricted fetuses (Lewi, 2013).


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Obstentrics_Williams. he cause of birthweight inequality in twin fetuses is often unclear, but the etiology in monochorionic twins likely difers from that in dichorionic twins. Because the single placenta is not always equally shared in monochorionic twins, these twins have greater rates of discordant growth outside of TTTS than dichorionic twins. Discordancy in monochorionic twins is usually attributed to placental vascular anastomoses that cause hemodynamic imbalance between the twins. Reduced pressure and perfusion of the donor twin can cause diminished placental and fetal growth. Even so, unequal placental sharing is probably the most important determinant of discordant growth in monochorionic twins (Lewi, 2013). Occasionally, monochorionic twins are discordant in size because they are discordant for structural anomalies.


Obstentrics_Williams

Obstentrics_Williams. Discordancy in dichorionic twins may result from various factors. Dizygotic fetuses may have diferent genetic growth potential, especially if they are of opposite genders. Second, because the placentas are separate and require more implantation space, one placenta might have a suboptimal implantation site. Bagchi and associates (2006) observed that the incidence of severe discordancy is twice as great in triplets as it is in twins. This finding lends credence to the view that in utero crowding is a factor in multifetal growth restriction. Placental pathology may playra role as well. In one study of 668 twin placentas, a strong relationship between histological placental abnormalities and birthweight discordancy was observed in dichorionic, but not monochorionic, twin pregnancies (Kent, 2012).


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Obstentrics_Williams. Size discordancy between twins can be determined sonographically. hat said, diferences in crown-rump length are not reliable predictors for birthweight discordance (Miller, 2012). hus, most begin surveillance for discordancy ater the first trimester. One common method uses sonographic fetal biometry to compute an estimated weight for each twin (Chap. 10, p. 184). The weight of the smaller twin is then compared with that of the larger twin. hus, percent discordancy is calculated as the weight of the larger twin minus the weight of the smaller twin, then divided by the weight of the larger twin. Alternatively, given that abdominal circumference (AC) relects fetal nutrition, some use the sonographic AC value of each twin.


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Obstentrics_Williams. With these methods, some diagnose selective fetal-growth restriction if the AC measurements difer more than 20 mm or if the estimated fetal weight diference is 20 percent or more. That said, several diferent weight disparities between twins have been used to deine discordancy. Accumulated data suggest that weight discordancy greater than 25 to 30 percent most accurately predicts an adverse perinatal outcome. At Parkland, Hollier and coworkers (1999) retrospectively evaluated 1370 delivered twin pairs and stratiied twin weight discordancy in 5-percent increments within a range of 15 to 40 percent. They found that the incidence of respiratory distress syndrome, intraventricular hemorrhage, seizures, periventricular leukomalacia, sepsis, and necrotizing enterocolitis rose directly with the degree of weight discordancy. Rates of these conditions grew substantially if discordancy exceeded 25 percent. The relative risk of fetal death increased significantly to 5.6 if discordancy was more


Obstentrics_Williams

Obstentrics_Williams. degree of weight discordancy. Rates of these conditions grew substantially if discordancy exceeded 25 percent. The relative risk of fetal death increased significantly to 5.6 if discordancy was more than 30 percent and rose to 18.9 if it was greater than 40 percent.


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Obstentrics_Williams. Sonographic monitoring of twin growth has become a mainstay in management. Monochorionic twins are generally monitored more frequently. his is because their risk of death is higher-3.6 percent versus 1.1 percent-and the risk of neurological damage in the surviving twin is substantial compared with those risks in dichorionic twins (Hillman, 2011; Lee, 2008). Thorson and colleagues (2011) retrospectively analyzed 108 monochorionic twin pregnancies and found that a sonographic evaluation interval > 2 weeks was associated with a higher Quintero stage at the time of TTTS diagnosis. hese indings have led some to recommend serial sonographic examination every 2 weeks in monochorionic twins (Simpson, 2013; Society for MaternalFetal Medicine, 2013). However, there have been no randomized trials of the optimal frequency of sonographic surveillance in monochorionic twin pregnancies. At Parkland Hospital, monochorionic twins undergo sonographic evaluation to assess interval growth every 4 weeks.


Obstentrics_Williams

Obstentrics_Williams. the optimal frequency of sonographic surveillance in monochorionic twin pregnancies. At Parkland Hospital, monochorionic twins undergo sonographic evaluation to assess interval growth every 4 weeks. In addition, a specific ultrasound examination to search for TTTS is completed at each intervening 2-week mark between these sonograms.


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Obstentrics_Williams. For dichorionic pregnancies, a recent report suggests that sonographic evaluation every 2 weeks would identiY more abnormalities prompting delivery (Corcoran, 2015). It has yet to be determined if this practice would improve perinatal outcomes. At our institution, dichorionic twins are sonographically evaluated every 6 weeks. Depending on the degree of discordancy and the gestational age, fetal surveillance may be indicated, especially if one or both fetuses exhibit restricted growth. Nonstress testing, biophysical profile, and umbilical artery Doppler assessment have all been recommended in the management of twins. However, none has been assessed in appropriately sized prospective trials (Miller, 2012).


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Obstentrics_Williams. If discordancy is identiied in a monochorionic twin pregnancy, umbilical artery Doppler studies in the smaller fetus may help guide management (Gratac6s, 2007). Namely, investigators have correlated umbilical artery Doppler results with placental indings and with the degree of selective fetal-growth restriction to predict fetal outcome (Gratac6s, 2012). hese correlations have yielded categories of selective fetal-growth restriction. Type I is characterized by positive end-diastolic low, a smaller degree of weight discordance, and a relatively benign clinical course. Type II displays persistently absent end-diastolic flow in the smaller twin and carries a high risk of deterioration and demise. Type III is intermittently absent or reversed end-diastolic flow. Because of large artery-to-artery anastomoses associated with the placentas in this category, type III is associated with a lower risk of deterioration than type II. In all evaluated cases, unequally shared placenta was noted to


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Obstentrics_Williams. anastomoses associated with the placentas in this category, type III is associated with a lower risk of deterioration than type II. In all evaluated cases, unequally shared placenta was noted to some degree.


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Obstentrics_Williams. With uncomplicated dichorionic multifetal gestations, use of antepartum surveillance has not improved perinatal outcomes. In sum, the American College of Obstetricians and Gynecologists (2016) recommends that antepartum testing be performed in multi fe tal gestations for indications similar to those for singleton fetuses (Chap. 17, p. 331). At Parkland, all women with twin discordancy :25 percent undergo daily monitoring as an inpatient. Data are limited to establish the optimal timing of delivery of twins for size discordancy alone. For those at advanced gestational ages, delivery can be pursued. • Death of One Fetus At any time during multifetal pregnancy, one or more fetuses may die, either simultaneously or sequentially. Causes and incidence of fetal death are related to zygosity, chorionicity, and growth concordance.


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Obstentrics_Williams. In some pregnancies, one fetus dies remote from term, but pregnancy continues with one or more live fetuses. When this occurs early in pregnancy, it may manifest as a vanishing twin, discussed on page 871. In a slightly more advanced pressed against the fetal membranes. Anatomical parts can be identified as marked. Demise of this twin had been noted during sonographic examination performed at 17 weeks' gestation. Its viable cotwin delivered at 40 weeks. (Used with permission from Dr. Michael V. Zaretsky.) gestation, fetal death may go undetected until delivery. In this case, delivery ofa normal newborn is followed by expulsion of a dead fetus that is barely identiiable. It may be compressed appreciably-'tus compressus, or it may be lattened remarkably through desiccation-'tuspapyraceus (Fig. 45-24).


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Obstentrics_Williams. As shown in Figure 45-25, the risk ofstillbirth is related to gestational age in all twins but is much higher for monochorionic twin pregnancies before 32 weeks' gestation. In a review of 9822 twin pregnancies, Morikawa and associates (2012) reported that 2.5 percent of monochorionic diamnionic twins �o 0: .� 15 ..0 FIGURE 45-25 Prospective risk of stillbirth among women who reached a given gestational week (per 1000 women). (Reproduced with permission from Morikawa M, Yamada 1, Yamada T, et al: Prospective risk of stillbirth: monochorionic diamniotic twins vs dichorionic twins, J Perinat Med. 2012 Jan 10;40(3):245-249.) greater than 22 weeks had a death of one or both twins. This compared with 1.2 percent of dichorionic twins. In this same review, women with monochorionic diamnionic twins who lost one twin were 16 times more likely to experience death of the cotwin than women with dichorionic twins who lost one twin. Other investigations have found similar trends (Danon, 2013;


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Obstentrics_Williams. Other investigations have found similar trends (Danon, 2013; Hillman, 2011; Mahony, 2011).


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Obstentrics_Williams. Hillman, 2011; Mahony, 2011). Other factors that afect the prognosis for the surviving twin include gestational age at the time of the demise and duration between the demise and delivery of the surviving twin. With a vanishing twin, the risk of death after the irst trimester is not increased for the survivor. However, when a fetus dies in the second trimester or later, the efect ofgestational age at the time ofdeath and the mortality risk to the cotwin are less clear. In an analysis by Hillman and colleagues (2011), cotwin demise rates were unafected regardless of whether the irst death occurred at 13 to 27 weeks' gestation or at 28 to 34 weeks. In cases with the death ofone twin after the irst trimester, however, the odds of spontaneous and iatrogenic preterm delivery of the remain ing living twin were increased (Hillman, 2011). Preterm birth gestation. Ifthe fetus died after 34 weeks, preterm delivery rates were similar.


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Obstentrics_Williams. The neurological prognosis for a surviving cotwin depends almost exclusively on chorionicity. In their comprehensive review, Ong and coworkers (2006) found an 18-percent rate of neurological abnormality in twins with monochorionic placentation compared with only 1 percent in those with dichorionic placentation. In another review, in twin pregnancies complicated by a single fetal demise before 34 weeks, a ivefold higher risk ofneurodevelopmental morbidity was identiied in monochorionic twins compared with dichorionic twins. If the one fetus died after 34 weeks, the likelihood ofneurological deicits was essentially the same between monochorionic and dichorionic twin pregnancies (Hillman, 201r1).


Obstentrics_Williams

Obstentrics_Williams. Later in gestation, the death ofone ofmultiple fetuses could theoretically trigger coagulation defects in the mother. Only a few cases of maternal coagulopathy after a single fetal death in a twin pregnancy have been reported. This is probably because the surviving twin is usually delivered within a few weeks ofthe demise (Eddib, 2006). That said, we have observed transient, spontaneously corrected consumptive coagulopathy in multifetal gestations in which one fetus died and was retained in utero along with its surviving twin. he plasma ibrinogen concentration initially decreased but then increased spontaneously, and the level of serum ibrinogen-ibrin degradation products increased initially but then returned to normal levels. At delivery, the portions of the placenta that supplied the living fetus appeared normal. In contrast, the part that had once provided for the dead fetus was the site of massive ibrin deposition.


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Obstentrics_Williams. Decisions should be based on gestational age, the cause of death, and the risk to the surviving fetus. First-trimester losses require no additional surveillance for this speciic indication. If the loss occurs after the irst trimester, the risk ofdeath or damage to the survivor is largely limited to monochorionic twin gestations. Morbidity in the monochorionic twin survivor is almost always due to vascular anastomoses, which often cause the demise of one twin followed by sudden hypotension in the other (p. 878). For this reason, if one fetus of a monochorionic twin gestation dies ater the first trimester but before viability, pregnancy termination can be considered (Blickstein, 2013). Occasionally, death of one but not all fetuses results from a maternal complication such as diabetic ketoacidosis or severe preeclampsia with abruption. Pregnancy management is based on the diagnosis and the status of both the mother and surviving fetus. If the death of one dichorionic twin is due to a


Obstentrics_Williams

Obstentrics_Williams. or severe preeclampsia with abruption. Pregnancy management is based on the diagnosis and the status of both the mother and surviving fetus. If the death of one dichorionic twin is due to a discordant congenital anomaly in the irst trimester, it should not afect the surviving twin.


Obstentrics_Williams

Obstentrics_Williams. Single fetal death during the late second and early third trimesters presents the greatest risk to the surviving twin. Although the risks of subsequent death or neurological damage to the survivor are comparatively higher for monochorionic twins at this gestational age, the risk of preterm birth is equally increased in mono-and dichorionic twins (Ong, 2006). Delivery generally occurs within 3 weeks of diagnosis of fetal demise, thus antenatal corticosteroids for survivor lung maturity should be considered (Blickstein, 2013). Regardless, unless the intrauterine environment is hostile, the goal is to prolong the preterm pregnancy.


Obstentrics_Williams

Obstentrics_Williams. Timing of elective delivery after conservative management of a late second-or early third-trimester single fetal death is debatable. Dichorionic twins can probably be safely delivered at term. Monochorionic twin gestations are more diicult to manage and are often delivered between 34 and 37 weeks' gestation (Blickstein, 2013). In cases of single fetal death at term, especially when the etiology is unclear, most opt for delivery instead of expectant management. The American College of Obstetricians and Gynecologists (2016) also endorse an individualized approach to such cases. • Impending Death of One Fetus


Obstentrics_Williams

Obstentrics_Williams. • Impending Death of One Fetus During antepartum surveillance tests of well-being, abnormal results in one twin, but not the other, pose a particular dilemma. Delivery may be the best option for the compromised fetus yet may result in death from immaturity of the cotwin. If fetal lung maturity is conirmed, salvage of both the healthy fetus and its jeopardized sibling is possible. Unfortunately, ideal management if twins are immature is problematic but should be based on the chances of intact survival for both fetuses. Often the compromised fetus is severely growth restricted or anomalous. Thus, performing amniocentesis for fetal chromosomal analysis in women of advanced maternal age carrying twin pregnancies is advantageous, even for those who would continue their pregnancies regardless of the diagnosis. Chromosomal abnormality identification in one fetus allows rational decisions regarding interventions.


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Obstentrics_Williams. With prenatal management of multifetal pregnancy, primary goals aim to prevent or interdict complications as they develop. A major imperative is to prevent preterm delivery of markedly immature neonates. At Parkland Hospital, women with multifetal gestations are seen every 2 weeks beginning at 22 weeks' gestation. A digital cervical examination is performed at each visit to screen for cervical shortening or dilation. Identification of other unique complications discussed earlier may also lead to interventions including admission or early delivery.


Obstentrics_Williams

Obstentrics_Williams. long with more frequent prenatal VISItS, the maternal diet should provide additional requirements for calories, protein, minerals, vitamins, and essential fatty acids. he Institute of Medicine (2009) recommends a 37-to 54-lb weight gain for women with twins and a normal BMI. In their review, Goodnight and Newman (2009) endorse supplementation of micronutrients such as calcium, magnesium, zinc, and vitamins C, D, and E. his is based on upper intake levels from the Food and Nutrition Board of the Institute of Medicine. he daily recommended augmented caloric intake for women with twins is 40 to 45 kcal/kg/d. Diets contain 20 percent protein, 40 percent carbohydrate, and 40 percent fat divided into three meals and three snacks daily.


Obstentrics_Williams

Obstentrics_Williams. As noted earlier (p. 882), serial sonographic examinations are usually performed throughout the third trimester to search for abnormal fetal growth and assess amnionic fluid volume. Associated oligohydramnios may indicate utero placental pathology and should prompt further evaluation of fetal well-being. That said, quantiYing amnionic luid volume in multifetal gestation is sometimes diicult. Some measure the deepest vertical pocket in each sac or assess the luid subjectively. Magann and coworkers (2000) compared subjective assessment and several objective methods of assessing amnionic fluid volume in 23 sets of twins. They found all methods to be equally poor in predicting abnormal volumes in diamnionic wins. At Parkland Hospital, the single deepest vertical pocket is measured in each sac. A measurement < 2 em is considered oligohydramnios, and a measurement > 8 cm is considered hydramnios (Duryea, 2017; Hernandez, 2012).


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Obstentrics_Williams. Of surveillance methods, the nons tress test or biophysical profile is often selected for twin or higher-order multifetal gestations. Because of the complex complications associated with these gestations and the potential technical diiculties in differentiating fetuses during antepartum testing, the usefulness of these methods appears limited. According to DeVoe (2008), the few exclusive studies of nonstress testing in twins suggest that the method performs the same as in singleton pregnancies. Elliott and Finberg (1995) used the biophysical profile as the primary method for monitoring higher-order multifetal gestations. They reported that four of 24 monitored pregnancies had a poor outcome despite reassuring biophysical proile scores. Although biophysical testing is commonly performed in multifetal gestations, there are insuicient data to determine its eicacy (DeVoe, 2008).


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Obstentrics_Williams. Similar indings have been reported with the addition of umbilical artery Doppler velocimetry in twins with concordant growth. For example, when umbilical artery Doppler velocime try was added to management compared with fetal testing based on fetal-growth parameters alone in the absence of growth dis cordance, perinatal outcomes were not improved (Giles, 2003). Likewise, Hack and associates (2008) investigated the utility mortality rates using pulsatility indices of the umbilical artery. tons, and data suggest that testing in multifetal gestations per forms no better. In cases of abnormal testing in one twin and normal results in another, iatrogenic preterm delivery remains a major concern. Options are similar to those described in the management of impending fetal death (p. 884).


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Obstentrics_Williams. Preterm labor is common in multifetal pregnancies and may complicate up to 50 percent of twin, 75 percent of triplet, and 90 percent of quadruplet pregnancies (Elliott, 2007). Similar to singleton preterm labor, intraamnionic infection is docu mented in approximately one third of twin pregnancy cases (Oh,r2017). In twins, the proportion of preterm births varies widely from 40 to 70 percent (Giufre, 2012). For example, black women have disparately higher risks for preterm delivery (Grant, 2017). • Prediction of Preterm Birth


Obstentrics_Williams

Obstentrics_Williams. A major goal of multi fetal prenatal care is accurate prediction of women likely to experience preterm delivery. Within the past decade, cervical length has been shown to be a potent predictor of preterm labor and delivery. To and associates (2006) so no graphically measured cervical length in 1163 twin pregnancies at 22 to 24 weeks' gestation. Rates of preterm delivery before 32 weeks were 66 percent in those with cervical lengths of 10 mm; 24 percent for lengths of 20 mm; and only 1 percent for 40 mm. In one review, Conde-Agudelo and coworkers (2010) concluded that a cervical length <20 mm was most accurate for predicting birth before 34 weeks, with a speciicity of 97 percent and positive likelihood ratio of 9.0. Kindinger and colleagues (2016) noted that prediction depended on both cervical length and gestational age at ascertainment. One study compared serial cervical length measurements with a single midgestation measurement. hese authors found that multiple assessments were more


Obstentrics_Williams

Obstentrics_Williams. length and gestational age at ascertainment. One study compared serial cervical length measurements with a single midgestation measurement. hese authors found that multiple assessments were more accurate to determine the risk of pre term twin birth in asymptomatic women (Melamed, 2016a). In another study, a change in cervical length :0.2 cm identified pregnancies at risk for delivery before 35 weeks (Moroz, 2017). Interestingly, a closed internal os by digital examination was found to be as predictive of postponed delivery as was the combination of a normal sonographically measured cervical length and negative fetal fibronectin test result (McMahon, 2002). Unfortunately, cervical length assessment in twin pregnancies has not been associated with improved outcomes (Gordon, 2016).


Obstentrics_Williams

Obstentrics_Williams. • Prevention of Preterm Birth Several schemes have been evaluated to prevent preterm labor and delivery. In recent years, some have been shown to decrease the risk of pre term delivery, but only in subgroups of singleton pregnancies. In general, most have been disappointingly ineffective for both singleton and multifetal pregnancies (American College of Obstetricians and Gynecologists, 2016). The bulk of evidence suggests that routine hospitalization does not prolong multifetal pregnancy. In one metaanaly sis, the practice did not reduce the risk of preterm birth or perinatal mortality (Crowther, 2010). At Parkland Hospital, elective hospitalization was compared with outpatient manage ment, and no advantages were found (Andrews, 1991). Impor tantly, however, almost half of women managed as outpatients required admission for specific indications such as hypertension or threatened preterm delivery.


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Obstentrics_Williams. Limited physical activity, early work leave, more frequent health-care visits and sonographic examinations, and structured advocated to reduce pre term birth rates in women with mul tiple fetuses. However, little evidence suggests that these mea sures substantially change outcome. his has not been studied extensively in multifetl pregnancies. In one review of prophylactic oral beta-mimetic therapy that included 374 twin pregnancies, treatment did not reduce the rate of twins delivering before 37 or before 34 weeks' gestation (Ymasmit, 2015). In light of the Food and Drug Administration warning against the use of oral terbutaline because of maternal side efects, the prophylactic use of beta-mimetic drugs in multifetal gestations seems unwarranted.


Obstentrics_Williams

Obstentrics_Williams. lthough somewhat efective in reducing recurrent preterm birth in women with a singleton pregnancy, weekly injections of 17 alpha-hydroxyprogesterone caproate (17 -OHP-C) are not efective for multifetal gestations (Caritis, 2009; Rouse, 2007). hese results were corroborated in a randomized trial of 240 twin pregnancies (Combs, 2011). Moreover, women carrying twins and having a cervical length <36 mm (25th percentile) did not beneit despite their greater risk for preterm birth (Durnwald, 2010). Senat and colleagues (2013) assigned 165 asymptomatic women with twins and a cervical length <25 mm to 17-0HP-C and also found no reduction in delivery rate before 37 weeks. Last, in an evaluation of plasma drug concentrations, higher concentrations of 17 -OHP-C were associated with earlier gestational age at delivery (Caritis, 2012). he authors concluded that 17-0HP-C may adversely lower the gestational age at delivery in women with twin gestations. In sum, administration of intramuscular 17


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Obstentrics_Williams. age at delivery (Caritis, 2012). he authors concluded that 17-0HP-C may adversely lower the gestational age at delivery in women with twin gestations. In sum, administration of intramuscular 17 -OHP-C to women with twin pregnancies, even to those with a shortened cervix, does not lower the preterm birth risk.


Obstentrics_Williams

Obstentrics_Williams. Micronized progesterone administered vaginally to women with twins to prevent preterm birth has provided conlicting results.


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Obstentrics_Williams. Cetingoz and coworkers (2011) gave 100 mg of micronized progesterone intravaginally daily from 24 to 34 weeks' gestation. his practice reduced rates of delivery before 37 weeks from 79 to 51 percent in 67 women with twins. In contrast, several studies have failed to demonstrate any preterm birth rate reduction in women receiving various formulations of vaginal progesterone. In the Prevention of Preterm Delivery in Twin Gestations (PREDICT) trial, 677 women with twins were randomly assigned to receive prophylactic, 200-mg progesterone pessaries or placebo pessaries (Rode, 2011). Progesterone failed to reduce delivery rates before 34 weeks. In a subgroup analysis that included only women with a short cervix or a history of prior preterm birth, also no benefit was found (Klein, 2011). Norman and colleagues (2009) also noted no lower rates of delivery before 34 weeks with progesterone gel treatment.


Obstentrics_Williams

Obstentrics_Williams. Romero and colleagues (2017) performed a metaanalysis of individual patient data for 303 women with twin gestation and a short cervix randomized to receive either vaginal progesterone or no treatment. They reported a significantly reduced risk of preterm birth before 30 weeks' gestation and improved composite perinatal outcomes in the treated women. Currently at Parkland Hospital, management of women with multifetal gestations does not typically include progestetone in any formulation. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) is currently enrolling patients into a randomized, placebo-controlled trial to further evaluate the use of micronized vaginal progesterone or the Arabin pessary, describe subsequently (PROSPECT, 2015). The primary outcome is delivery prior to 35 weeks or fetal loss.


Obstentrics_Williams

Obstentrics_Williams. Prophylactic cerclage does not improve perinatal outcome in women with multifetal pregnancies. Studies have included women who were not specially selected but also those who were selected because of a shortened cervix that was identified sonographically (Houlihan, 2016; Newman, 2002; Rebarber, 2005). Indeed, in the latter group, cerclage may actually worsen outcomes (Berghella, 2005; Roman, 2013). Rescue cerclage in women with a second-trimester twin gestation and a dilated cervix may be beneficial. Roman and coworkers (2016) reported a retrospective cohort study in which women undergoing rescue cerclage had significantly better neonatal outcomes than those without cerclage.


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Obstentrics_Williams. A vaginal pessary that encircles and theoretically compresses the cervix, alters the inclination of the cervical canal, and relieves direct pressure on the internal cervical os has been proposed as an alternative to cerclage. One of the most popular is the silicone Arabin pessary. In a study of its use in women with a short cervix between 18 and 22 weeks' gestation, a subgroup analysis of 23 women with twins showed a signiicant reduction in the delivery rate before 32 weeks compared with the rate in 23 control pregnancies (Arabin, 2003). In another randomized trial, women treated with a cervical pessary had signiicantly fewer births before 34 weeks (Goya, 2016).


Obstentrics_Williams

Obstentrics_Williams. Other studies have been less favorable. In the randomized Pessaries in Multiple Pregnancy as a Prevention of Preterm Birth (ProTWIN) trial, 813 un selected women with twins received either the Arabin pessary between 12 and 20 weeks or no treatment (Liem, 2013). The pessary failed to reduce preterm birth overall but did decrease delivery rates before 32 weeks-29 versus 14 percent-in a subset of women with a cervical length <38 mm. Similar results were reported from a randomized multicenter trial with a total of 11r80 twin pregnancies (Nicolaides, 2016). A smaller randomized study using a Bioteque cup pessay showed no diference in outcomes (Berghella, 2017). At this time, pessary use is not recommended by the merican College of Obstetricians and Gynecologists (2016). As noted above, results from the ongoing PROSPECT trial are anticipated to provide more data. • Treatment of Preterm Labor


Obstentrics_Williams

Obstentrics_Williams. Although many advocate their use, therapy with tocolytic agents to forestall preterm labor in multifetal pregnancy does not result in measurably improved neonatal outcomes (Chauhan, 2010; Gyetvai, 1999). Another caveat is that tocolytic therapy in women with a multifetal pregnancy entails higher risks than in singleton pregnancy. This stems in part from augmented pregnancy-induced hypervolemia, which raises cardiac demands and increases the susceptibility to iatrogenic pulmonary edema (Chap. 47, p. 917). Gabriel and colleagues (1994) compared outcomes of 26 twin and six triplet pregnancies with those of 51 singletons-all treated with a beta-mimetic drug for preterm labor. Women with a multifetal gestation had significantly more cardiovascular complications-43 versus 4 percent-including three gravidas with pulmonary edema. In a retrospective analysis, Derbent and coworkers (2011) evaluated nifedipine tocolysis in 58 singleton and 32 twin pregnancies. hese authors reported higher


Obstentrics_Williams

Obstentrics_Williams. three gravidas with pulmonary edema. In a retrospective analysis, Derbent and coworkers (2011) evaluated nifedipine tocolysis in 58 singleton and 32 twin pregnancies. hese authors reported higher incidences of side efects such as maternal tachycardia in women with twins-19 versus 9 percent.


Obstentrics_Williams

Obstentrics_Williams. Administration of corticosteroids to stimulate fetal lung maturation has not been well studied in multifetal gestation. However, these drugs logically should be as beneicial for multiples as they are for singletons (Roberts, 2006). In a large retrospective study evaluating betamethasone therapy eicacy in preterm twin versus preterm singleton pregnancies, no diferences in neonatal morbidity between the two groups were identiied (Melamed, 2016b). Gyamfi and associates (2010) evaluated betamethasone concentrations in women receiving weekly antenatal corticosteroids and found no diferences in levels between twins and singletons. Conversely, another study found lower cord/maternal ratios of dexamethasone in twin versus singleton pregnancies (Kim, 2017). hese treatments are discussed in Chapter 42 (p. 823). At this time, guidelines for the use of these agents do not difer from those for singleton gestations (American College of Obstetricians and Gynecologists, 2016).


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Obstentrics_Williams. The frequency of preterm premature rupture of membranes (PPROM) rises with increasing plurality. In a populationbased study of more than 290,000 live births, the proportion of preterm birth complicated by premature rupture was 13.2 percent in singletons (Pakrashi, 2013). This rate compared with rates of 17, 20, 20, and 100 percent in twins, triplets, quadruplets, and even higher-order multiples, respectively. Multifetal gestations with PPROM are managed expectantly similar to singleton pregnancies (Chap. 42, p. 820). Ehsanipoor and colleagues (2012) compared outcomes of 41 twin and 82 singleton pregnancies, both with ruptuted membranes between 24 and 32 weeks. They found the median number of days to subsequent delivery was overall shorter for twins-3.6 days compared with 6.2 days for singletons. This latency diference was significant in pregnancies after 30 weeks-l.7 days and 6.9 days. Importantly, latency beyond 7 days approximated 40 percent in both groups.


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• Delayed Delivery of Second Twin

Obstentrics_Williams. • Delayed Delivery of Second Twin


Obstentrics_Williams

Obstentrics_Williams. Infrequently, after preterm birth of the presenting fetus, it may be advantageous for undelivered fetus(es) to remain in utero. Trivedi and Gillett (1998) reviewed 45 case reports of asynchronous birth in multifetal gestations. Although reported outcomes may relect bias, pregnancies with a surviving retained twin or triplet continued for an average of 49 days. No advantage was gained by management with tocolytics, prophylactic antimicrobials, or cerclage. In their 10-year experience, Roman and associates (2010) reported a median latency of 16 days in 13 twin and ive triplet pregnancies with delivery of the irst fetus between 20 and 25 weeks' gestation. Survival of the irstborn neonate was 16 percent. Although 54 percent of the retained fetuses survived, only 37 percent of survivors did so without major morbidity. Livingston and coworkers (2004) described 14 pregnancies in which an active attempt was made to delay delivery of 19 fetuses after delivery of the irst neonate. Only one


Obstentrics_Williams

Obstentrics_Williams. so without major morbidity. Livingston and coworkers (2004) described 14 pregnancies in which an active attempt was made to delay delivery of 19 fetuses after delivery of the irst neonate. Only one fetus survived without major sequelae, and one mother developed sepsis syndrome with shock. Arabin and van Eyck (2009) reported better outcomes in a few of the 93 twin and 34 triplet pregnancies that qualiied for delayed delivery in their center during a 17 -year period.


Obstentrics_Williams

Obstentrics_Williams. If asynchronous birth is attempted, there must be careful evaluation for infection, abruption, and congenital anomalies. The mother must be thoroughly counseled, particularly regarding the potential for serious, life-threatening infection. The range of gestational age in which the beneits outweigh the risks for delayed delivery is likely narrow. Avoidance of delivery from 23 to 26 weeks would seem most beneficial. In our experience, good candidates for delayed delivery are rare. A litany of complications may be encountered during labor and delivery of multiple fetuses. In addition to preterm birth, rates of uterine contractile dysfunction, abnormal fetal presentation, umbilical cord prolapse, placenta previa, placental abruption, emergent operative delivery, and postpartum hemorrhage from uterine atony are higher. All of these must be anticipated, and thus certain precautions and special arrangements are prudent. These should include the following. 1.


Obstentrics_Williams

Obstentrics_Williams. 1. An appropriately trained obstetrical attendant should remain with the mother throughout labor. Continuous electronic monitoring is preferable. If membranes are ruptured and the cervix dilated, the presenting fetus is monitored internally. 2. An intravenous infusion system capable of delivering fluid rapidly is established. In the absence of hemorrhage, lactated Ringer or an aqueous dextrose solution is infused at a rate of 60 to 125 mLlhr. 3. Blood for transfusion is readily available if needed. 4. n obstetrician skilled in intrauterine identification of fetal parts and in intrauterine manipulation of a fetus should be present. 5. A sonography machine is readily available to evaluate the presentation and position of the fetuses during labor and to image the remaining fetus(es) after delivery of the irst. 6.


Obstentrics_Williams

Obstentrics_Williams. 5. A sonography machine is readily available to evaluate the presentation and position of the fetuses during labor and to image the remaining fetus(es) after delivery of the irst. 6. An anesthesia team is immediately available in the event that emergent cesarean delivery is necessary or that intrauterine manipulation is required for vaginal delivery. 7. For each fetus, at least one attendant who is skilled in resuscitation and care of newborns and who has been appropriately informed of the case should be immediately available. 8. he delivery area should provide adequate space for the nursing, obstetrical, anesthesia, and pediatric team members to work efectively. Equipment must be on site to provide emergent anesthesia, operative intervention, and maternal and neonatal resuscitation. • Timing of Delivery


Obstentrics_Williams

Obstentrics_Williams. • Timing of Delivery Several factors afect this timing and include gestational age, fetal growth, lung maturity, and presence of maternal complications. As measured by determination of the lecithin-sphingomyelin ratio, pulmonary maturation is usually synchronous in twins (Leveno, 1984). Moreover, although this ratio usually does not exceed 2.0 until 36 weeks in singleton pregnancies, it oten exceeds this value by approximately 32 weeks in multifetal pregnancies. Similar increased values of surfactant have been noted in twins after 31 weeks' gestation (McElrath, 2000). In a comparison of respiratory morbidity in 100 twins and 241 singleton newborns delivered by cesarean before labor, Ghi and associates (2013) found less neonatal respiratory morbidity in twins, especially those delivered <37 weeks' gestation. In some cases, however, pulmonary function may be markedly diferent, and the smallest, most stressed twin fetus is typically more mature.


Obstentrics_Williams

Obstentrics_Williams. At the other end of the spectrum, Bennett and Dunn (1969) suggested that a twin pregnancy of 40 weeks or more should be considered postterm. Twin stillborn neonates delivered at 40 weeks or beyond commonly had features similar to those of postmature singletons (Chap. 43, p. 836). From an analysis of almost 300,000 twin births, at and beyond 39 weeks, the risk of subsequent stillbirth was greater than the risk of neonatal mortality (Kahn, 2003).


Obstentrics_Williams

Obstentrics_Williams. From their guidelines, the American College of Obstetricians and Gynecologists (2016) recommends delivery at 38 weeks for uncomplicated dichorionic twin pregnancies. Women with uncomplicated monochorionic diamnionic twin pregnancies can undergo delivery between 34 and weeks. And, for women with monoamnionic twin pregnancies, delivery is recommended at 32 to 34 weeks. At Parkland Hospital, we generally follow these recommendations but do not routinely deliver monochorionic diamnionic twin pregnancies before 37 weeks unless another obstetrical indication develops. • Evaluation of Fetal Presentation


Obstentrics_Williams

Obstentrics_Williams. In addition to the standard preparations for the conduct oflabor and delivery discussed in Chapter 22, there are special considerations for women with a multifetal pregnancy. First, the positions and presentations of fetuses are best confirmed sonographically. Although any possible combination of positions may be encountered, those most common at admission for delivery are cephalic-cephalic, cephalic-breech, and cephalic-transverse. At Parkland Hospital between 2008 and 2013, 71 percent of twin pregnancies had a cephalic presentation of the irst fetus at the time of admission to labor and delivery. Importantly, with perhaps the exception of cephalic-cephalic presentations, these are all unstable before and during labor and delivery. Accordingly, compound, face, brow, and footling breech presentations are relatively common, and even more so if fetuses are small, amnionic luid is excessive, or maternal parity is high. Cord prolapse is also frequent in these circumstances.


Obstentrics_Williams

Obstentrics_Williams. After this initial evaluation, if active labor is conirmed, then a decision is made to attempt vaginal delivery or to proceed with cesarean delivery. The latter is usually chosen because of fetal presentations. In general, cephalic presentation of the irst fetus in a laboring woman with twins may be considered for vaginal delivery (American College of Obstetricians and Gynecologists, 2016). The proportion of women undergoing an attempted vaginal delivery varies greatly depending on the skills of the delivering physician (de Castro, 2016; Easter, 2017; Schmitz, 2017). Still, the cesarean delivery rate is high. For example, of the 547 women with the irst twin presenting cephalic who were admitted to Parkland Hospital during 5 years, only 32 percent were delivered spontaneously. And, the overall cesarean delivery rate in twin pregnancies during those years was 77 percent. Notably, 5 percent of cesareans performed were for emergent delivery of the second twin following vaginal delivery of


Obstentrics_Williams

Obstentrics_Williams. cesarean delivery rate in twin pregnancies during those years was 77 percent. Notably, 5 percent of cesareans performed were for emergent delivery of the second twin following vaginal delivery of the first twin. The desire to avoid this obstetrical dilemma has contributed to the rising cesarean delivery rate in twin pregnancies across the United States (Antsalis, 2013).


Obstentrics_Williams

Obstentrics_Williams. After a comparison of 891 twins with more than 100,000 singleton pregnancies included in the Consortium of Safe Labor, Leftwich and colleagues (2013) concluded that active labor progressed more slowly in both nulliparas and multiparas with twins. Provided women with twins meet all criteria for oxytocin administration, it may be used as described in Chapter 26 (p. 509). Wolfe and associates (2013) evaluated the success of labor induction and concluded that oxytocin alone or in combination with cervical ripening can safely be used in twin gestations. Taylor and coworkers (2012) reported similar results. Conversely, Razavi and colleagues (2017) found that maternal morbidity was increased with labor induction. In an analysis of twin births in the United States, induction rates of twin pregnancies have decreased from a maximum of 13.8 percent in 1999 to 9.9 percent in 2008 (Lee, 2011). Generally, at Parkland Hospital we do not induce or augment labor in women with a multifetal gestation.


Obstentrics_Williams

Obstentrics_Williams. have decreased from a maximum of 13.8 percent in 1999 to 9.9 percent in 2008 (Lee, 2011). Generally, at Parkland Hospital we do not induce or augment labor in women with a multifetal gestation. In suitable candidates with a strong desire for vaginal birth, amniotomy induction has been one option.


Obstentrics_Williams

Obstentrics_Williams. During labor and delivery of multiple fetuses, decisions regarding analgesia and anesthesia may be complicated by problems imposed by preterm labor, preeclampsia, desultory labor, need for intrauterine manipulation, and postpartum uterine atony and hemorrhage. Labor epidural analgesia is ideal because it provides excellent pain relief and can be rapidly extended cephalad if internal podalic version or cesarean delivery is required. If general anesthesia becomes necessary for intrauterine manipulation, uterine relxation can be accomplished rapidly with one of the halogenated inhalation agents discussed in Chapter 25 (p. 499). Some clinicians use intravenous or sublingual nitroglycerin or intravenous terbutaline to achieve uterine relaxation yet avoid the risks associated with general anesthetics. hese agents are usually best administered by the anesthesia team.


Obstentrics_Williams

Obstentrics_Williams. Regardless of fetal presentation during labor, obstetricians must be ready to deal with any change of fetal position during delivery. This is especially true following delivery of the first twin. Importantly, related to delivery method, second twins at term have worse composite neonatal outcomes compared with outcomes of their cotwin regardless of delivery method (Muleba, 2005; Smith, 2007; Thorngren-Jerneck, 2001). If the first twin presents cephalic, delivery can usually be accomplished spontaneously or with forceps. According to D'Alton (2010), there is general consensus that a trial oflabor is reasonable in women with cephalic-cephalic twins. From their review, Hogle and associates (2003) found that planned cesarean delivery does not improve neonatal outcome when both twins are cephalic. The randomized trial by Barrett and coworkers (2013) airms this conclusion.


Obstentrics_Williams

Obstentrics_Williams. The optimal delivery route for cephalic-noncephalic twin pairs remains controversial. Patient selection is crucial, and options include cesarean delivery of both twins, or less commonly, vaginal delivery with intrapartum external cephalic version of the second twin. Longer intertwin delivery time has been shown in some studies to be associated with poorer second twin outcome (Edris, 2006; Stein, 2008). Thus, breech extraction may be preferable to version. Least desirable, vaginal delivery of the first but cesarean delivery of the second twin may be required due to intrapartum complications such as umbilical cord prolapse, placental abruption, contracting cervix, or fetal distress. ·Most but not all studies report the worst composite fetal out comes for this scenario (Alexander, 2008; Rossi, 2011; Wen, 2004).