Obstentrics_Williams

Obstentrics_Williams. Ureteropelvic Junction Obstruction. This condition is the most common abnormality associated with renal pelvis dilatation. The birth prevalence is 1 in 1000 to 2000, and males are afected three times more often than females (Williams, 2007; Woodward, 2002). Obstruction is generally functional rather than anatomical, and it is bilateral in up to a fourth of cases. he likelihood of ureteropelvic junction obstruction rises from 5 percent with mild renal pelvis dilatation to more than 50 percent with severe dilatation (Lee, 2006).


Obstentrics_Williams

Obstentrics_Williams. Duplicated Renal Collecting System. In this anatomical anomaly, the upper and lower poles of the kidney-called moieties-are each drained b) a separate ureter (Fig. 10-42). Duplication is found in approximately 1 in 4000 pregnancies, is more common in females, and is bilateral in 15 to 20 percent of cases (James, 1998; Vergani, 1998; Whitten, 2001). Sonographically, an intervening tissue band separates two distinct renal pelves. Development of hydronephrosis or ureteral dilatation may occur due to abnormal implantation of one or both ureters within the bladder-a relationship that reflects the anatomical Weigert-Meyer rule. The upper pole ureter may develop obstruction from a ureterocele within the bladder, whereas the lower pole ureter has a shortened intravesical segment that predisposes to vesicoureteral reflux (see Fig. 10-42B). Thus, both moieties may become dilated from diferent etiologies, and both are at risk for loss of function.


Obstentrics_Williams

Obstentrics_Williams. The prevalence of bilateral renal agenesis is approximately in 8000 births, whereas that of unilateral renal agenesis is 1 in FIGURE 10-42 Duplicated renal collecting system. The upper and lower moieties of the kidney are each drained by a separate ureter. A. Renal pelvis dilatation is visible in both the upper (U) and lower (L) pole moieties, which are separated by an intervening band of renal tissue (arrowhead). B.The bladder, encircled by the highlighted umbilical arteries, contains a ureterocele (arrowhead). 1000 births (Cragan, 2009; Dolk, 2010; Sheih, 1989; Wiesel, 2005). When a kidney is absent, color Doppler imaging of the descending aorta demonstrates absence of the ipsilateral renal artery (Fig. 10-43). In addition, the ipsilateral adrenal gland typically enlarges to ill the renal fossa, termed the ying down adrenal sin (Hofman, 1992). As with other fetal anomalies, amniocentesis for chromosomal microarray analysis should be considered.


Obstentrics_Williams

Obstentrics_Williams. If renal agenesis is bilateral, no urine is produced, and the resulting anhydramnios leads to pulmonary hypoplasia, limb contractures, and a distinctively compressed face. When this combination results from renal agenesis, it is called Poter syndrome, after Dr. Edith Potter, who described it in 1946. When these abnormalities result from severely decreased amnionic luid volume from another etiology, such as bilateral multicystic dysplastic kidney or autosomal recessive polycystic kidney disease, it is called Poter sequence. he prognosis for these abnormalities is extremely poor.


Obstentrics_Williams

Obstentrics_Williams. This severe form of renal dysplasia results in a nonfunctioning kidney. The nephrons and collecting ducts do not form normally, such that primitive ducts are surrounded by ibromuscular tissue, and the ureter is atretic (Hains, 2009). Sonographically, the kidney contains numerous smooth-walled cysts of varying size that do not communicate with the renal pelvis and are surrounded by echogenic cortex (Fig. 10-44). Unilateral multicystic dysplastic kidney (MCDK) has a prevalence of 1 in 4000 births. Contralateral renal abnormalities are present in 30 to 40 percent-most frequently vesicoureteral relux or ureteropelvic junction obstruction (Schreuder, 2009). Nonrenal anomalies have been reported in 25 percent of cases, and cystic dysplasia may occur as a component of many genetic syndromes (Lazebnik, 1999; Schreuder, 2009). If MCDK is isolated and unilateral, the prognosis is generally good.


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-43 Renal agenesis. A.oln this coronal image of the fetal abdomen, color Doppler shows the course of the abdominal aorta. The ultrasound beam is perpendicular to the aorta, demonstrating absence of the renal arteries bilaterally. B. This coronal image of a fetus with unilateral renal agenesis shows the adrenal gland (arrowheads) filling the renal fossa, termed the "lying-down" adrenal sign. The adrenal gland has a hypoechoic cortex and hyperechoic medulla. FIGURE 10-44 Multicystic dysplastic kidneys. Coronal view of the fetal abdomen demonstrates markedly enlarged kidneys containing multiple cysts of varying sizes that do not communicate with a renal pelvis. FIGURE 10-45 Posterior urethral valve. In this 19-week fetus with severe bladder outlet obstruction, the bladder is dilated and thickwalled, with dilatation of the proximal urethra that resembles a "keyhole." Adjacent to the bladder is an enlarged kidney with evidence of cystic dysplasia, conferring a poor prognosis.


Obstentrics_Williams

Obstentrics_Williams. Bilateral MCDK is found in approximately 1 in 12,000 births. It is associated with severely decreased amnionic luid volume starting early in gestation. his leads to Potter sequence and a poor prognosis (Lazebnik, 1999).


Obstentrics_Williams

Obstentrics_Williams. Of the hereditary polycystic diseases, only the infantile form of autosomal recessive poyystic kidney disease (APD) may be reliably diagnosed prenatally. ARPKD is a chronic, progressive disease of the kidneys and liver that results in cystic dilatation of the renal collecting ducts and in congenital hepatic ibrosis (Turkbey, 2009). he carrier frequency of a disease-causing mutation in the PHDI gene approximates 1 in 70, and the disease prevalence is 1 in 20,000 (Zerres, 1998). he phenotypic variability of ARPKD ranges from lethal pulmonary hypoplasia at birth to presentation in late childhood or even adulthood with predominantly hepatic manifestations. Sonographically, infantile ARPKD displays abnormally large kidneys that ill and distend the fetal abdomen and have a solid, ground-glass texture. Severe oligohydramnios confers a poor prognosis.


Obstentrics_Williams

Obstentrics_Williams. Autosomal dominant poyystic kidney disease ADPD), which is far more common, usually does not manifest until adulthood (Chap. 53, p. 1031). Even so, some fetuses with AD PKD have mild renal enlargement and enhanced renal echogenicity in the setting of normal amnionic luid volume. he diferential diagnosis for these findings includes several genetic syndromes, aneuploidy, or normal variant.


Obstentrics_Williams

Obstentrics_Williams. Distal obstruction of the urinary tract is more frequent in male fetuses, and the most common etiology is posterior urethral valves. Characteristically, the bladder and proximal urethra are dilated, termed the "keyhole" sign, and the bladder wall is thick (Fig. 10-45). Oligohydramnios, particularly before midpregnancy, portends a poor prognosis because of pulmonary hypoplasia. Unfortunately, the outcome may be poor even with normal amnionic fluid volume. Evaluation includes a careful search for associated anomalies, which may occur in 40 percent of cases, and for aneuploidy, which has been reported in 5 to 8 percent (Hayden, 1988; Hobbins, 1984; Mann, 2010). If neither are present, afected male fetuses with severe oligohydramnios who have fetal urinary electrolytes suggesting a potentially favorable prognosis may be fetal therapy candidates. Evaluation and treatment of fetal bladder outlet obstruction is discussed in Chapter 16 (p. 325).


Obstentrics_Williams

Obstentrics_Williams. The 2015 revision of the Nosology and Classification of Genetic Skeletal Disorders includes an impressive 436 skeletal anomalies in 42 groups, characterized by genetic abnormalities, phenotypic features, or radiographic criteria (Bonafe, 2015). he two types of skeletal dysplasias are osteochondrodyspasiasthe generalized abnormal development of bone and/or cartilage, and dysostoses-which are abnormalities of individual bones, for example, poydacyy. In addition to these maormations, skeletal abnormalities include dormations, as with some cases of clubfoot, and disruptions such as limb-reduction defects. The prevalence of skeletal dysplasias approximates 3 in 10,000 births. Two groups account for more than half of all cases: the ibroblast growth octor 3 (FGF3) chondrodysplasia group and the osteogenesis impeecta and decreased bone density group. Each occurs in 0.8 in 10,000 births (Stevenson, 2012).


Obstentrics_Williams

Obstentrics_Williams. Evaluation of a pregnancy with suspected skeletal dysplasia includes a survey of every long bone, as well as the hands and feet, skull size and shape, clavicles, scapulae, thorax, and spine. Reference tables are used to determine which long bones are afected and ascertain the degree of shortening (Appendix, p. 1267). Involvement of all long bones is termed micromelia, whereas predominant involvement of only the proximal, intermediate, or distal long bone segments is termed rhizomelia, meso melia, and acromelia, respectively. he degree of ossiication should be noted, as should presence of bowing or fractures. Each of these may provide clues to narrow the diferential diagnosis and occasionally suggest a specific skeletal dysplasia. Many, if not most, skeletal dysplasias have a genetic component, and knowledge of specific mutations has advanced dramatically (Bonafe, 2015).


Obstentrics_Williams

Obstentrics_Williams. nosis, it is frequently possible to determine whether a skeletal dysplasia is lethal. Lethal dysplasias show profound long bone shortening, with measurements <5th percentile, and display cent (Nelson, 2014; Rahemtullah, 1997; Ramus, 1998). Gen erally, other sonographic abnormalities are evident. Pulmonary hypoplasia is suggested by a thoracic circumference < 80 per cent of the abdominal circumference value, by a thoracic cir cumference <2.5th percentile, and a cardiac circumference > 50 percent of the thoracic circumference value (Appendix, p. 1266). Afected pregnancies also may develop hydramnios and/or hydrops (Nelson, 2014).


Obstentrics_Williams

Obstentrics_Williams. he FGFR3 chondrodysplasias include achondroplasia and thanatophoric dysplasia. Achondroplasia, also called heterozygous achondroplasia, is the most common nonlethal skeletal dysplasia. An impressive 98 percent of cases are due to a speciic point mutation in the FGFJ gene. It has an autosomal dominant inheritance, and 80 percent of cases result from a new mutation. Achondroplasia is characterized by long bone shortening that is predominantly rhizomelic, an enlarged head with frontal bossing, depressed nasal bridge, exaggerated lumbar lordosis, and a trident configuration of the hands. Intelligence is typically normal. Sonographically, the femur and humerus measurements may not lie below the 5th percentile until the early third trimester. hus, this condition is usually not diagnosed until late in pregnancy. In homozygotes, which represent 25 percent of the ofspring of heterozygous parents, the condition is characterized by greater long bone shortening and is lethal.


Obstentrics_Williams

Obstentrics_Williams. he other major class of FGFR3 dysplasias, thanatophoric dysplasia, is the most common lethal skeletal disorder. It is characterized by severe micromelia, and afected fetuses-particularly those with type II-may develop a characteristic cloverleaf skull deformity (Kleeblattschade) due to craniosynostosis. More than 99 percent of cases may be con firmed with genetic testing. Osteogenesis impeecta represents a group of skeletal dysplasias typiied by hypomineralization. here are multiple types, and more than 90 percent of cases are characterized by a mutation in the COLIAI or COLIA2 gene. Type IIa, also called the perinatal form, is lethal. It displays a profound lack of skull ossification, such that gentle pressure on the maternal abdomen from the ultrasound transducer results in visible skull deformation 10-46).


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-46 Osteogenesis imperfecta. Type Ila, which is lethal, is characterized by such profound lack of skull ossification that gentle pressure on the maternal abdomen from the ultrasound transducer results in visible deformation (flattening) of the skull (arrowheads). Other features include multiple in-utero fractures and ribs that appear "beaded." Inheritance is autosomal dominant, such that all cases result from either new mutations or gonadal mosaicism (Chap. 13, p. 264). Another skeletal dysplasia that results in severe hypomineralization is hypophosphatasia, which has an autosomal recessive inheritance.


Obstentrics_Williams

Obstentrics_Williams. his disorder is notable for a deformed talus and shortened Achilles tendon. he afected foot is abnormally fixed and positioned with equinus (downward pointing), varus (inward rotation), and forefoot adduction. Most cases are considered malformations, with a multifactorial genetic component. However, an association with environmental factors and with early amniocentesis suggests that deformation also plays a role (T redwell, 2001). Sonographically, the footprint is visible in the same plane as the tibia and ibula (Fig. 10-47).


Obstentrics_Williams

Obstentrics_Williams. he prevalence of clubfoot approximates 1 in 1000 births, and the male:female ratio is 2:1 (Carey, 2003; Pavone, 2012). Clubfoot is bilateral in approximately 50 percent of afected individuals, and associated anomalies are present in at least 50 percent of all cases (lvfammen, 2004; Sharma, 201i1). Frequently associated anomalies include neuraltube defects, arthrogryposis, and myotonic dystrophy and other genetic syndromes. In cases with associated anomalies, aneuploidy is found in approximately 30 percent. In contrast, the rate is <4 percent when clubfoot appears isolated (Lauson, 2010; Sharma, 2011). hus, a careful search for associated structural abnormalities is warranted, and chromosomal microarray analysis may be considered. FIGURE 10-47 Foot position. A. Normal fetal lower leg, demonstrating normal position of the foot. B. With talipes equinovarus, the foot "print" is visible in the same plane as the tibia and fibula.


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-47 Foot position. A. Normal fetal lower leg, demonstrating normal position of the foot. B. With talipes equinovarus, the foot "print" is visible in the same plane as the tibia and fibula. Documentation of the arms and legs is a component of the standard examination. he absence or hypoplasia of all or part of one or more extremities is a limb-reduction dect. he birth prevalence is 4 to 8 in 10,000 (Kucik, 2012; Stoll, 2010; Vasluian, 2013). Approximately half of these are isolated defects, up to on� third occur as part of a recognized syndrome, and individuals in the remaining cases have other coexisting anomalies (Stoll, 2010; Vasluian, 2013). Upper extremities are afected more frequently than lower ones. Of categories, a terminal transverse limb dect lacks part or all of a distal limb to create a stump (Fig. 10-48). his is more common than a longitudinal dect, which is complete or partial absence of the long bone(s) on only one side of a given extremity.


Obstentrics_Williams

Obstentrics_Williams. Absence of an entire extremity is termed amelia. Phocomelia, associated with thalidomide exposure, is an absence of one or more long bones with the hands or feet attached to the trunk (Chap. 12, p. 246). Limb-reduction defects are associated with numerous genetic syndromes, such as Roberts syndrome, an autosomal recessive condition characterized by tetraphocomelia. A clubhand dormiy, usually from an absent radius, is associated with trisomy 18 and is also a component of the thrombocytopenia-absent radius syndrome (Fig. 13-5B, p. 258). Limb-reduction defects may occur in the setting of a disruption such as amnionic-band sequence (Chap. 6, p. 116). hey have also been associated with chorionic villus sampling when performed before 10 weeks' gestation (Fig. 14-6, p. 294).


Obstentrics_Williams

Obstentrics_Williams. During the past two decades, three-dimensional (3-D) sonography has gone from a novelty to a standard feature of most modern ultrasound equipment (Fig. 10-49). 3-D sonography is not routiney used during a standard examination nor considered a required modality. However, it may be a component of specialized evaluations. Most 3-D scanning uses a special transducer developed for this purpose. After a region of interest is identiied, a 3-D volume is acquired that can be rendered to display axial, sagittal, coronal, or oblique images. Sequential "slices" may be generated, similar to computed tomographic (CT) or MR images. Unlike two-dimensional (2-D) scanning, which appears to be in "real time," 3-D imaging is static and obtained by processing a volume of stored images. With our-dimensional (4-DJ sonography, also known as real-time 3-D sonography, rapid reconstruction of the rendered images conveys the impression that the scanning is in real time.


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-48 Transverse limb-reduction defect. A. At 18 weeks' gestation, only a rudimentary hand was visible. B. By 24 weeks, the radius and ulna were normal in size and appearance, and small rudimentary digits were evident.


Obstentrics_Williams

Obstentrics_Williams. For 4-D imaging, one application known as spatiotemporal image co rrelatio n-S TIC improves visualization of cardiac anatomy. During an automated sweep over the heart, the STIC application acquires a volume that includes thousands of 2D images captured at a rate as high as 150 frames per second (Devore, 2003). These individual images are obtained at diferent locations in the heart but at the same point in time. These views are subsequently arranged according to their spatial and temporal domains. his permits display of an ordered sequence of volume sets in a continuous cine loop (or video clip) of the cardiac cycle (Yeo, 2016). For example, after obtaining a volume sweep over the cardiac apex, an application such as Fetal Intelligent Navigation Echocardiography (FINE) can be applied to FIGURE 10-49 Fetal face. Surface rendered three-dimensional image of a normal fetal face and hand at 32 weeks. display videos of each of the diferent cardiac views shown in


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-49 Fetal face. Surface rendered three-dimensional image of a normal fetal face and hand at 32 weeks. display videos of each of the diferent cardiac views shown in Fig. 10-28 (Garcia, 2016). It is hoped that such technology may eventually improve detection of fetal cardiac anomalies. For selected anomalies, such as those of the face and skel eton, for tumors, and for some cases of neural-tube defects, 3-D sonography can add useful information (American College of


Obstentrics_Williams

Obstentrics_Williams. Obstetricians and Gynecologists, 2016; Goncalves, 2005). That said, comparisons of 3-D and conventional 2-D sonography for the diagnosis of most congenital anomalies have not demon strated better overall detection rates (Goncalves, 2006; Reddy, 2008). The American College of Obstetricians and Gynecolo gists (2016) concludes that proof of a clinical advantage of 3-D S sonography for prenatal diagnosis is generally lacking. D hen sound waves strike a moving target, the frequency of the waves reflected back is shifted in proportion to the velocity and direction of that moving target-a phenomenon known as the Doppler sht. Because the magnitude and direction of the frequency shift depend on the relative motion of the moving target, Doppler can help evaluate low within blood vessels. The Doppler equation is shown in Figure 10-50.


Obstentrics_Williams

Obstentrics_Williams. n important component of the equation is the angle of insonation, abbreviated as theta (8). This is the angle between the sound waves from the transducer and low within the vessel. Measurement error becomes large when 8 is not close to zero, in other words, when blood flow is not coming directy toward or away from the transducer. For this reason, ratios are often used to compare diferent waveform components, allowing cosine 8 to cancel out of the equation. Figure 10-51 is a schematic of the Doppler waveform and describes the three ratios commonly used. he simplest is the systolic-diastolic ratio (SID ratio), which compares the maximal (or peak) systolic low with end-diastolic flow to evaluate downstream impedance to flow. Currently, two types of Doppler modalities are available for clinical use. Continuous-wave Doppler equipment has two separate types of crystals-one transmits high-frequency sound waves, and ,,,I ,


Obstentrics_Williams

Obstentrics_Williams. Continuous-wave Doppler equipment has two separate types of crystals-one transmits high-frequency sound waves, and ,,,I , FIGURE 10-50 Doppler equation. Ultrasound emanating from the transducer with initial frequency fo strikes blood moving at velocity v. Reflected frequency fd is dependent on angle e between beam of sound and vessel. FIGURE 10-51 Doppler systolic-diastolic waveform indices of blood flow velocity. S represents the peak systolic flow or velocity, and D indicates the end-diastolic flow or velocity. The mean, which is the time-average mean velocity, is calculated from computerdigitized waveforms. another continuously captures signals. In M-mode imaging, continuous-wave Doppler is used to evaluate motion through time, however, it cannot image individual vessels.


Obstentrics_Williams

Obstentrics_Williams. another continuously captures signals. In M-mode imaging, continuous-wave Doppler is used to evaluate motion through time, however, it cannot image individual vessels. Pulsed-wave Doppler uses only one crystal, which transmits the signal and then waits until the returning signal is received before transmitting another one. It allows precise targeting and visualization of the vessel of interest. Pulsed-wave Doppler can be conigured to allow color-low mapping-such that blood flowing toward the transducer is displayed in red and that flowing away from the transducer appears in blue. Various combinations of pulsed-wave Doppler, color-flow Doppler, and real-time sonography are commercially available.


Obstentrics_Williams

Obstentrics_Williams. Umbilical artery Doppler has been subjected to more rigorous assessment than any previous test of fetal health. he umbilical artery difers from other vessels in that it normally has forward low throughout the cardiac cycle. Moreover, the amount of low during diastole increases as gestation advances, and this reflects decreasing placental impedance. As a result, the SID ratio normaly declines rom approximatey 4.0 at 20 weeks' gestation, to generaly less than 3.0 ter 30 weeks' and inaly to 2.0 at term. Because of downstream impedance to low, more end-diastolic low is observed at the placental cord insertion than at the fetal ventral wall. hus, abnormalities such as absent or reversed enddiastolic low will appear first at the fetal cord insertion site. The International Society of Ultrasound in Obstetrics and Gynecology recommends that umbilical artery Doppler measurements be made in a free loop of cord (Bhide, 2013). However, assessment close to the ventral wall insertion may optimize


Obstentrics_Williams

Obstentrics_Williams. in Obstetrics and Gynecology recommends that umbilical artery Doppler measurements be made in a free loop of cord (Bhide, 2013). However, assessment close to the ventral wall insertion may optimize measurement reproducibility when low is diminished (Berkley, 2012).


Obstentrics_Williams

Obstentrics_Williams. The waveform is considered abnormal if the SID ratio is >95th percentile for gestational age. In extreme cases of growth restriction, end-diastolic flow can become absent or even reversed (Fig. 44-8, p. 854). Such reversal of end-diastolic flow has been associated with greater than 70-percent obliteration of the small muscular arteries in placental tertiary stem villi (Kingdom, 1997; Morrow, 1989). As described in Chapter 44 (p. 854), umbilical artery Doppler aids management of fetal-growth restriction and has been associated with improved outcome in these cases (American College of Obstetricians and Gynecologists, 2015). It is not recommended for complications other than growth restriction. Similarly, its use for growth-restriction screening is not advised (Berkley, 2012). Abnormal umbilical artery Doppler findings should prompt a complete fetal evaluation, if not already done, because abnormal measurements are associated with major fetal anomalies and aneuploidy (Wenstrom, 1991).


Obstentrics_Williams

Obstentrics_Williams. Doppler evaluation of the ductus arteriosus has been used primarily to monitor fetuses exposed to indomethacin and other nonsteroidal antiinlammatory agents (NSAIDs). Indomethacin, which is used by some for tocolysis, may cause ductal constriction or closure, particularly when used in the third trimester (Huhta, 1987). The resulting increased pulmonary flow can cause reactive hypertrophy of the pulmonary arterioles and eventual development of pulmonary hypertension. In a review of 12 randomized controlled trials involving more than 200 exposed pregnancies, Koren and coworkers (2006) reported that NSAIDs raised the odds of ductal constriction 15-fold. When these agents are indicated, their duration is typically limited to less than 72 hours. And, women taking NSAIDs are closely monitored so that these can be discontinued if ductal constriction is identified. Fortunately, ductal constriction is often reversible after NSAID discontinuation.


Obstentrics_Williams

Obstentrics_Williams. Uterine blood low is estimated to rise from 50 mLlmin early in gestation to 500 to 750 mLlmin by term. he uterine artery Doppler waveform is characterized by high diastolic low velocities and markedly turbulent flow. Greater resistance to flow and development of a diastolic notch are associated with later development of gestational hypertension, preeclampsia, and fetal-growth restriction. Zeeman and coworkers (2003) also found that women with chronic hypertension who had elevated uterine artery impedance at 16 to 20 weeks' gestation were at greater risk to develop superimposed preeclampsia. However, the technique, best testing interval, and defining criteria for this indication have not been standardized. As the predictive value of uterine artery Doppler testing is considered to be low, its use for screening or for clinical decision-making is not recommended in either high-risk or low-risk pregnancies (Sciscione, 2009).


Obstentrics_Williams

Obstentrics_Williams. Doppler interrogation of the middle cerebral artery (MCA) has been investigated and applied clinically for fetal anemia detection and fetal-growth restriction evaluation. Anatomically, the path of the MCA is such that flow often approaches the transducer "head-on," allowing for accurate determination of low velocity (Fig. 10-52). he MCA is imaged in an axial view of the head at the base of the skull, ideally within 2 mm of the internal carotid artery origin. Velocity measurement is optimal when the insonating angle is close to zero, and no more than 30 degrees of angle correction should be used. In general, velocity assessment is not performed in other fetal vessels, because a larger insonating angle is needed and confers significant measurement error.


Obstentrics_Williams

Obstentrics_Williams. When fetal anemia is present, the peak systolic velociy is enhanced due to greater cardiac output and decreased blood viscosity (Segata, 2004). This has permitted the reliable, noninvasive detection of fetal anemia in cases of blood-group alloimmunization. Mari and colleagues (2000) demonstrated that an MCA peak systolic velocity threshold of 1.50 MoM could reliably identiy fetuses with moderate or severe anemia. As discussed in Chapter 15 (p. 303), MCA peak systolic velocity has replaced FIGURE 10-52 Middle cerebral artery (MCA) Doppler. A. Color Doppler of the circle of Willis, demonstrating the correct location to sample the MCA. B. The waveform demonstrates a peak systolic velocity exceeding 70 cm/sec in a 32-week fetus with severe fetal anemia secondary to Rh alloimmunization. invasive testing with amniocentesis as the preferred test for fetal anemia detection (Society for Maternal-Fetal Medicine, 2015).


Obstentrics_Williams

Obstentrics_Williams. invasive testing with amniocentesis as the preferred test for fetal anemia detection (Society for Maternal-Fetal Medicine, 2015). MCA Doppler has also been studied as an adjunct in evaluation of fetal-growth restriction. Fetal hypoxemia is believed to result in increased blood flow to the brain, heart, and adrenal glands, leading to greater end-diastolic low in the MCA. his phenomenon, "brain-sparing," is actually a misnomer, as it is not protective for the fetus but rather is associated with perinatal morbidity and mortality (Bahado-Singh, 1999; CruzMartinez, 2011). The utility ofMCA Doppler to aid the timing of delivery is uncertain. It has not been evaluated in randomized trials or adopted as standard practice in the management of growth restriction (American College of Obstetricians and Gynecologists, 2015; Berkley, 2012).


Obstentrics_Williams

Obstentrics_Williams. he ductus venosus is imaged as it branches from the umbilical vein at approximately the level of the diaphragm. Fetal position poses more of a challenge in imaging the ductus venosus than it does with either the umbilical artery or the middle cerebral artery. he waveform is biphasic and normally has forward flow throughout the cardiac cycle. The irst peak reflects ventricular systole, and the second is ventricular diastolic illing. These are followed by a nadir during atrial contraction-termed the a-wave.


Obstentrics_Williams

Obstentrics_Williams. It is believed that Doppler indings in preterm fetuses with growth restriction show a progression in which umbilical artery Doppler abnormlities are followed by ones in the middle cerebral artery and then in the ductus venosus. However, manifestations of these abnormalities vary widely (Berkley, 2012). With severe fetal-growth restriction, cardiac dysfunction may lead to low in the a-wave that is decreased, absent, and eventually reversed, along with pulsatile low in the umbilical vein (Fig. 10-53).


Obstentrics_Williams

Obstentrics_Williams. Ductus venosus abnormalities have potential to identiy preterm growth-restricted fetuses that are at greatest risk for adverse outcomes (Baschat, 2003, 2004; Bilardo, 2004; Figueras, 2009). As noted by the Society for Maternal-Fetal Medicine, however, they have not been suiciently evaluated in randomized trials (Berkley, 2012). In sum, Doppler assessment of vessels other than the umbilical artery has not been shown to improve perinatal outcome, and thus their role in clinical practice remains uncertain (American College of Obstetricians and Gynecologists, 2015).


Obstentrics_Williams

Obstentrics_Williams. Image resolution with MR is oten superior to that with sonography because it is not as hindered by bony interfaces, maternal obesity, oligohydramnios, or an engaged fetal head. Thus, it can serve as an adjunct to sonography in evaluating suspected fetal abnormalities. Examples include complex abnormalities of the fetal CNS, thorax, gastrointestinal system, genitourinary system, and musculoskeletal system. MR has also been used in the evaluation of maternal pelvic masses and placental invasion. MR imaging, however, is not portable, it is time-consuming, and its use is generally limited to referral centers with expertise in fetal imaging. To guide clinical use, the American College of Radiology and Society for Pediatric Radiology (2015) have developed


Obstentrics_Williams

Obstentrics_Williams. To guide clinical use, the American College of Radiology and Society for Pediatric Radiology (2015) have developed FIGURE 10-53 Venous Doppler abnormalities. A. Reversal of a-wave flow in the ductus venosus. Arrows depict a-waves below the baseline. This finding may be identified with cardiac dysfunction in the setting of severe fetal-growth restriction. B. Pulsatile flow in the umbilical vein. The undulating umbilical venous waveform below the baseline indicates tricuspid regurgitation. Above the baseline is the umbilical artery waveform, in which there is no visible end-diastolic flow. Because the venous waveform is below the baseline in this image, it is not possible to determine whether the umbilical artery end-diastolic flow is reversed.


Obstentrics_Williams

Obstentrics_Williams. a practice guideline for fetal MR imaging. This document acknowledges primacy of sonography as the preferred screening modality. Moreover, it recommends that fetal MR imaging be used for problem solving to ideally contribute to prenatal diagnosis, counseling, treatment, and delivery planning. Specific indications for fetal MR imaging are listed in Table 10-11 and are discussed subsequently. MR imaging uses no ionizing radiation, but theoretical concerns include the efects of luctuating electromagnetic ields and high sound-intensity levels. The strength of the magnetic TABLE 10-11. Fetal Conditions for Which Magnetic Resonance Imaging May Be Indicateda Agenesis of the corpus callosurn Solid or cyJtic masses Vascular malformations Hydranencephaly Infarction. Hemorrhage Skull, face, and neck Other abnormalities with potential airway obstruction Evaluation of pulmonary hypoplasia secondary to diaphragmatic hernia, oligohydramnios, chest mass, or ske!etal dysplasia


Obstentrics_Williams

Obstentrics_Williams. Skull, face, and neck Other abnormalities with potential airway obstruction Evaluation of pulmonary hypoplasia secondary to diaphragmatic hernia, oligohydramnios, chest mass, or ske!etal dysplasia Abdomen, pelvis, and retroperitoneum Abdominopelvic cystic mass evaluation Tumor evaluation (sacrococcygeal teratoma, neuroblastoma, hemangioma, suprarenal or renal masses) Complex genitourinary anomalies (bladder outlet obstruction syndromes, bladder exstrophy, cloacal exstrophy) Assess rena! anomalies with oligohydramnios Diagnose bowel anomalies (anorectal malformations, Complications of monochorionic twins Determine vascular anatomy prior to laser treatment Assess morbidity ater death of a monochorionic co-twin


Obstentrics_Williams

Obstentrics_Williams. Diagnose bowel anomalies (anorectal malformations, Complications of monochorionic twins Determine vascular anatomy prior to laser treatment Assess morbidity ater death of a monochorionic co-twin Fetal brain anatomy before and after surgical intervention Anomalies for which fetal surgery is planned aln some cases, magnetic resonance (MR) imaging is indicated only if the anomaly is ed but cannot be adequately characterized sonographically, vvhich is assessed on a case-by case basis. Data from American College of Radiology, 2015.


Obstentrics_Williams

Obstentrics_Williams. Data from American College of Radiology, 2015. field is measured in tesLa (), and most imaging studies during pregnancy are performed using 1.5 T. A few preliminary studies advocate the use of 3 T for fetal imaging to potentially improve signal-to-noise ratios and thus image clarity (Victoria, 2016). For safety, all clinical examinations must adhere to the speciic absorption rate, which is regulated by the Food and Drug Administration, and the ALARA principle should be followed. Thus, for routine clinical examinations, the lower ield strength of 1.5 T is recommended (Prayer, 2017).


Obstentrics_Williams

Obstentrics_Williams. Human and tissue studies support the safety of fetal MR imaging. Repetitive exposure of human lung fibroblasts to a static 1.5-T magnetic ield does not afect cellular proliferation (Wiskirchen, 1999). Fetal heart rate patterns have been evaluated before and during MR imaging, and no signiicant diferences were observed (Vadeyar, 2000). Children exposed to MR as fetuses do not show a greater incidence of disease or disability when tested at age 9 months or 3 years (Baker, 1994; Clements, 2000).


Obstentrics_Williams

Obstentrics_Williams. Glover and associates (1995) attempted to mimic the sound level experienced by the fetal ear by having an adult volunteer swallow a microphone while the stomach was illed with a liter of luid to represent the amnionic sac. Sound intensity was attenuated at least 30-dB from the body surface to the fluidfilled stomach and reduced the sound pressure from 120 dB to below 90 dB. This level is considerably less than the 135 dB experienced from vibroacoustic stimulation used in antepartum well-being assessments (Chap. 17, p. 337). Cochlear function testing in infants exposed to 1.5-T MR imaging as fetuses showed no hearing impairment (Reeves, 2010).


Obstentrics_Williams

Obstentrics_Williams. he American College of Radiology (2013) concludes that based on available evidence, MR imaging has no documented deleterious efects on the developing fetus. Therefore, MR imaging can be performed in pregnancy if data are needed to care for the fetus or mother. Health-care providers who are pregnant may work in and around an MR unit, but it is recommended that they not remain in the MR scanner magnet room-known as Zone IV-while an examination is in progress.


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Obstentrics_Williams. Gadolinium-based MR contrast agents are gadolinium (Gd3+) chelates. These contrast agents readily enter the fetal circulation and are excreted via fetal urination into amnionic luid, where they may remain for an indeterminate period before being ingested and reabsorbed. he longer the gadolinium-chelate molecule remains in a protected space such as the amnionic sac, the greater the potential for dissociation of the toxic Gd3+ ion. Accordingly, gadolinium contrast should be avoided during pregnancy because of this potential for dissociation. Routine use of gadolinium is not recommended unless there are overwhelming potential benefits (American College of Radiology, 2013). In adults with renal disease, this contrast agent has been associated with development of nephrogenic systemic fibrosis, a potentially severe complication.


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Obstentrics_Williams. Before MR examination, all women complete a written safety questionnaire that includes information about metallic implants, pacemakers, or other metal-or iron-containing devices that may alter the study (American College of Radiology, 2013). Iron supplementation may cause artifact in the colon but does not usually afect the resolution of fetal images. In more than nancy during the past 15 years, maternal anxiety secondary to claustrophobia and/or fear of MR equipment has developed in less than 1 percent of our patients. To reduce maternal anxiety in this small group, a single oral dose of diazepam, 5 to 10 mg, or lorazepam, 1 to 2 mg, may be given.


Obstentrics_Williams

Obstentrics_Williams. To begin an MR examination, women are placed in a supine or left lateral decubitus position. A torso coil is used in most circumstances to send and receive the radiofrequency pulses, but a body coil can be used alone to accommodate large mater nal habitus. A series of three-plane localizers, or scout views, are obtained relative to the maternal coronal, sagittal, and axial planes. he gravid uterus is imaged in the maternal axial plane (7-mm slices, 0 gap) with a T2-weighted fast acquisition. Typically, these may be a single-shot fast spin echo sequence (SSFSE), half-Fourier acquisition single-shot turbo spin echo (HASTE), or rapid acquisition with relaxation enhancement (AE), depending on the brand of machine. Next, a fast T1-weighted acquisition such as spoiled gradient echo (SPGR) is performed (7-mm thickness, 0 gap). hese large-field-of-view acquisitions through the maternal abdomen and pelvis are par ticularly good for identiying fetal and maternal anatomy.


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Obstentrics_Williams. Orthogonal images of targeted fetal or maternal structures are then obtained. In these cases, 3-to 5-mm slice thickness, o gap T2-weighted acquisitions are performed in the coronal, sagittal, and axial planes. Depending on the anatomy and underlying suspected abnormality, T1-weighted images can be performed to evaluate for subacute hemorrhage, fat, or location of normal structures that appear bright on these sequences, such as liver and meconium in the colon (Brugger, 2006; Zaretsky, 2003b).


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Obstentrics_Williams. Short Tl inversion recovey (STIR) and frequency-selective fat-saturated T2-weighted images may provide diferentiation in cases in which the water content of the abnormality is similar to that of the normal structure. An example is a thoracic mass compared with normal lung. Difusion-weighted imaging may be employed to evaluate for restricted difusion, which can be seen in ischemia, cellular tumors, or clotted blood (Brugger, 2006; Zaretsky, 2003b). Our series also includes an axial brain 3-to 5-mm T2-weighted sequence to obtain head biometry for gestational age estimation using the biparietal diameter and head circumference (Reichel, 2003).


Obstentrics_Williams

Obstentrics_Williams. Whenever a fetal abnormality is identiied, indings from the afected organ and other organ systems should be thoroughly characterized. Accordingly, a fetal anatomical survey is generally completed during each MR examination. In a recent prospective study, nearly 95 percent of the anatomical components recommended by the Inter- national Society of Ultrasound in Obstetrics and Gynecology were visible at 30 weeks' gestation (Millischer, 2013). he aorta and pulmonary artery were the most diicult to evaluate. Zaretsky and coworkers (2003a) similarly found that with the exclusion of cardiac structures, fetal anatomical evaluation was possible in 99 percent of cases. For intracranial anomalies, very fast T2-weighted images produce excellent tissue contrast, and eSF-containing structures are hyperintense or bright. This allows exquisite detail of the posterior fossa, midline structures, and cerebral cortex. T1-weighted images are used to identiy hemorrhage.


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Obstentrics_Williams. eNS biometry obtained with MR imaging is comparable with that obtained using sonography (Twickler, 2002). Nomograms have been published for multiple intracranial structures, including corpus callosum and cerebellar vermis lengths (Garel, 2004; Tilea, 2009). MR imaging provides valuable added information for cerebral abnormalities suspected sonographically (Benacerraf, 2007; Li, 2012). In early studies, MR imaging changed the diagnosis in 40 to 50 percent of cases and afected management in 15 to 50 percent (Levine, 1999b; Simon, 2000; Twickler, 2003). Additional information is more likely to be gained when the examination is performed beyond 24 weeks' gestation. More recently, Griiths and associates (2017) reported that MR evaluation of suspected fetal brain anomalies identified additional indings in nearly 50 percent and changed prognosis in 20 percent.


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Obstentrics_Williams. Fetuses with a cerebral abnormality may have a signiicant lag in cortical development. Levine and colleagues (l999a) demonstrated that MR imaging accurately portrays cerebral gyration and sulcation patterns (Fig. 10-54). Sonography permits limited evaluation of subtle migrational abnormalities, and MR imaging provides greater accuracy, particularly later in gestation. For ventriculomegaly, fetal MR imaging is selected to help identiy associated underlying eNS dysmorphology (p. 193). In cases of septo-optic dysplasia, MR imaging may confirm absence of the septum pellucidum and display hypoplastic FIGURE 10-54 Axial images of the fetal brain at 23 weeks' gestation (A) and at 33 weeks (8) demonstrate the normal gyration and sulcation progression during fetal development. These images were obtained using a Half Fourier Acquisition Single Shot Turbo Spin Echo (HASTE) sequence because it is relatively motion insensitive.


Obstentrics_Williams

Obstentrics_Williams. optic tracts (Fig. 10-55). In other fetuses, MR imaging can also assist with identiying agenesis or dysgenesis of the corpus callosum and characterizing migrational abnormalities (Benacerraf, 2007; Li, 2012; Twickler, 2003). Another fetal MR imaging indication is evaluation of suspected intraventricular hemorrhage (IVH). Fetal IVH risk factors include atypical-appearing ventriculomegaly, neonatal alloimmune thrombocytopenia, and a monochorionic multifetal gestation complicated by demise of one fetus or by severe twin-twin transu FIGURE 10-55 Septo-optic dysplasia. Axial (A) and coronal (B) images at 30 weeks' ges sion syndrome (Hu, 2006). If hemorrhage tation confirm absence of the cavum septum pellucidum (arrowheads) in both. There is is seen, MR imaging characteristics may also associated mild ventriculomegaly (arrow).


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Obstentrics_Williams. FIGURE 10-56 Terminal myelocystocele, 36 weeks' gestation. A. In this sagittal T2-weighted image, the spinal cord is tethered, expanding into the terminal cyst (arrow). B. Seen in this Tl-weighted image, the meningocele and terminal cyst are covered by subcutaneous fat (arrows) and skin. indicate which structures are involved and approximately when bleeding occurred. In the setting of congenital fetal infections, ,1R imaging can delineate the variable degrees of neural parenchymal abnormality and subsequent maldevelopment (Soares de Oliveira-Szejnfeld, 2016). Aside from cerebral structure, suspected spinal dysraphisms, including neural-tube defects, can also be further characterized for surgical planning. Figure 10-56 demonstrates a complex skin-covered dysraphism with associated tethering of the spinal cord. his terminal myelocystocele will benefit from early intervention following delivery.


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Obstentrics_Williams. Many thoracic abnormalities are readily seen with targeted sonography. MR imaging, however, may help delineate the location and size of space-occupying thoracic lesions and quantiy remaining lung tissue volumes. MR imaging can aid in characterizing the type of congenital cystic adenomatoid malformation and in visualizing the blood supply of pulmonary sequestration (p. 200). With congenital diaphragmatic hernia, MR imaging can help veriy and quantiy the abdominal organs within the thorax. his includes the volume of herniated liver and compressed lung tissue volumes (Fig. 10-57) (Debus, 2013; Lee, 2011; Mehollin-Ray, 2012). Also in fetuses with diaphragmatic hernia, MR imaging can assist in identiying other organ-system abnormalities, which may greatly afect fetal prognosis (Kul, 2012). MR imaging similarly is used for chest evaluation in skeletal dysplasia and to measure lung volumes in pregnancies with prolonged oligohydramnios secondary to renal disease or ruptured membranes


Obstentrics_Williams

Obstentrics_Williams. MR imaging similarly is used for chest evaluation in skeletal dysplasia and to measure lung volumes in pregnancies with prolonged oligohydramnios secondary to renal disease or ruptured membranes (Messerschmidt, 2011; Zaretsky, 2005).


Obstentrics_Williams

Obstentrics_Williams. When sonographic viewing of fetal abdominal abnormalities is limited by oligohydramnios or maternal obesity, MR imaging may add value (Caire, 2003). Hawkins and coworkers (2008) found that lack of signal in a contracted fetal bladder on T2-weighted sequences was associated with lethal renal abnormalities (Fig. 10-58). Diferences in signal characteristics between meconium in the fetal colon and urine in the bladder may permit deinition of cystic abdominal abnormalities (Farhataziz, 2005). Given the predictable pattern of meconium accumulation within the gastrointestinal tract and high signal intensity on T1-weighted sequences, MR imaging is a complementary tool in diagnosing gastrointestinal abnormalities and complex cloacal malformations (Furey, 2016). Peritoneal calciications related to meconium peritonitis are more readily apparent


Obstentrics_Williams

Obstentrics_Williams. FIGURE 10-57 A. Coronal image of normal lungs on a balanced sequence at 29 weeks' gestation. The liver (L) and stomach (5) lie below the diaphragm. B. Left-sided congenital diaphragmatic hernia (CDH) (dotted ellipse) seen on balanced sequence at 33 weeks. C. The T1o-weighted sequence confirms the subdiaphragmatic position of the liver and better delineates the small bowel (arrow) and meconium-containing colon (arrowhead) that have herniated into the chest. D. Another image of a left-sided CDH at 22 weeks demonstrates no normal lung, the heart (H) displaced into the right chest, and an elevated liver (dotted ellipse). sonographically, whereas pseudocysts and resultant abnormalities of meconium migration are better delineated with MR imaging . • Adjunct to Fetal Therapy


Obstentrics_Williams

Obstentrics_Williams. As indications for fetal therapy have grown, MR imaging is used preoperatively to outline abnormalities. At some centers, before laser ablation of placental anastomoses for twin-twin transfusion syndrome, MR imaging is performed to assess the fetal brain for IVH or periventricular leukomalacia (Chap. 45, p. 878) (Hu, 2006; Kline-Fath, 2007). Because of its precision in visualizing brain and spine indings in cases of myelomeningocele, it is often used preoperatively. For sacrococcygeal teratomas, if fetal surgery is considered, MR imaging may identiY tumor extension into the fetal pelvis (Avni, 2002; Neubert, 2004; Perrone, 2017). With a fetal neck mass for which an EIT is considered, MR imaging may help delineate the lesion extent and its efect on the oral cavity, hypopharynx, and trachea (Hirose, 2003; Lazar, 2012; Ogamo, 2005; Shiraishi, 2000). Finally, vfR imaging can also calculate a jaw index when an EIT procedure may be needed for severe micrognathia (MacArthur, 2012; Morris,


Obstentrics_Williams

Obstentrics_Williams. (Hirose, 2003; Lazar, 2012; Ogamo, 2005; Shiraishi, 2000). Finally, vfR imaging can also calculate a jaw index when an EIT procedure may be needed for severe micrognathia (MacArthur, 2012; Morris, 2009). Fetal therapy is discussed in Chapter 16 (p. 327).


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Obstentrics_Williams. FIGURE 10-58 A. Sagittal short T1 inversion recovery (STIR) image through a fetus with posterior urethral valve at 23 weeks' gestation. Notice the characteristic dilation of the posterior urethra (arrowhead). B. At 31 weeks, a coronal image shows progression of severe hydronephrosis, cystic changes in the parenchyma, hydroureter, and anhydramnios. The lungs (L) show a decreased signal and are small. C. An axial balanced sequence shows a distended bladder (B) with thickened wall (arrows). The clinical importance of identiying women with placenta accreta is discussed in Chapter 41 (p. 777). Sonography is gen erally used to identiy placental invasion into the myometrium, however, MR evaluation is an adjunct for indeterminate cases.


Obstentrics_Williams

Obstentrics_Williams. bands on T2-weighted images, focal bulging, and placental heterogeneity (Leyendecker, 2012). When used in a comple mentary role, MR imaging sensitivity is high for detection of placental invasion, although the depth of invasion is diicult to predict. Clinical risk factors and sonographic indings should be taken into account when interpreting MR placental images.


Obstentrics_Williams

Obstentrics_Williams. Of these, MR difusion tensor imaging and tractography may allow urther understanding of neural development and more precise definition of abnormality and pathology (Kasprian, 2008; Mitter, 2015). Automatic and semiautomated extraction of quantitative data from MR imaging volumetric acquisitions of fetal brain and placenta may enable subanalyses of massive datasets not previously possible with laborious manual segmentation (Tourbier, 2017; Wang, 2016). Using multiparametric MR of the placenta in vivo will expand our understanding of function and pathology without risk to mother or fetus. Last, although echocardiography will always be paramount in fetal heart assessment, MR imaging may contribute to volumetric cardiac analysis and will urther evaluation of the aorta, which is oten diicult to completely examine sonographically (Lloyd, 2017).


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Obstentrics_Williams. Adzick NS, Harrison MR, Glick PL, et al: Fetal cystic adenomatoid malformation: prenatal diagnosis and natural history. J Pediatr Surg 20:483, 1985 Al-Kaf A, MacDonald Sc, Kent N, et al: Delivery planning for pregnancies with gastroschisis: findings from a prospective national registry. Am J Obstet Gynecole213(4):557.e1,e2015 Altman P, Randolph JG, Lilly JR: Sacrococcygeal teratoma: American Academy of Pediatrics Surgical Section survey-1973. J Pediatr Surg 9:389, 1974 American College of Obstetricians and Gynecologists: Fetal growth restriction. Practice Bulletin No. 134, May 2013, Reairmed 2015 American College of Obstetricians and Gynecologists: Ultrasound in pregnancy. Practice Bulletin No. 175, December 2016


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Obstentrics_Williams. Practice Bulletin No. 134, May 2013, Reairmed 2015 American College of Obstetricians and Gynecologists: Ultrasound in pregnancy. Practice Bulletin No. 175, December 2016 American College of Obstetricians and Gynecologists: Management of suboptimally dated pregnancies. Committee Opinion No. 688, March 2017a American College of Obstetricians and Gynecologists: Methods for estimating the due date. Committee Opinion No. 700, May 20e17b American College of Radiology: Expert Panel on MR Saety: ACR guidance document on MR safe practices. J Magn Reson Imaging 37:501,e2013


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Obstentrics_Williams. American College of Radiology and Society for Pediatric Radiology: ACR-SPR practice guideline for the safe and optimal performance of fetal magnetic resonance imaging. Resolution No. 11, 2015. Available at: https://www.acr.org/ -/ medilCB384A65345F402083639E6756CE513F .pdf Accessed July 10, 2017 American Institute of Ultrasound in Medicine (AlUM): Oicial statements. Prudent use in pregnancy. 2012. Available at: http://www.aium.org/oicalStatements/33. Accessed July H), 2017 American Institute of Ultrasound in Medicine (AlUM): Oicial statements. Statement on the safe use of Doppler ultrasound during 11-14 weeks scans (or earlier in pregnancy). 2016. Available at: http://ww.aium.org/ oicialStatements/42. Accessed September 16, 20e17 American Institute of Ultrasound in Medicine (AlUM): Practice guideline for rhe performance offetal echo cardiography. J Ultrasound Med 32(6): 1067, 2013a American Institute of Ultrasound in Medicine (AlUM): Practice guideline for the performance of obstetric


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Obstentrics_Williams. guideline for rhe performance offetal echo cardiography. J Ultrasound Med 32(6): 1067, 2013a American Institute of Ultrasound in Medicine (AlUM): Practice guideline for the performance of obstetric ultrasound examinations. J Ultrasound Med 32(6):1083,e2013b


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Obstentrics_Williams. Avni FE, Guibaus L, Robert Y, et al: MR imaging of fetal sacrococcygeal teratoma: diagnosis and assessment. AJR Am J Roentgenol 178(1): 179, 2002 Axt-Fliedner R, Schwarze A, Smrcek J, et al: Isolated ventricular septal defects dated by color Doppler imaging: evolution during fetal and first year of postnatal life. Ultrasound Obstet Gynecol 27:266, 2006 Azizkhan RG, Crombleholme TM: Congenital cystic lung disease: contemporary antenatal and postnatal management. Pediatric Surg Int 24:643, 2008 Bahado-Singh RO, Kovanci E, Jefres A, et al: he Doppler cerebroplacental ratio and perinatal outcome in intrauterine growth restriction. Am J Obstet GynecoIe180(3):750, 1999 Baker PN, Johnson IR, Harvey PR, et al: A three-year follow-up of children imaged in utero with echo-planar magnetic resonance. Am J Obstet Gynecol 170:32, 1994


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Obstentrics_Williams. Baschat A: Doppler application in the delivery timing of the preterm growthrestricted fetus: another step in the right direction. Ultrasound Obstet GynecoIe23:1e11,e2004 Baschat A: Relationship between placental blood low resistance and precordial venous Doppler indices. Ultrasound Obstet Gynecol 22:561, 2003 Benacerraf BR, Shipp TO, Bromley B, et al: What does magnetic resonance imaging add to the prenatal sonographic diagnosis of ventriculomegaly? J Ultrasound Med 26:1513,e2007 Berkley E, Chauhan SP, Abuhamad A: Society for Maternal-Fetal Medicine Clinical Guideline: Doppler assessment of the fetus with intrauterine growth restriction. Am J Obstet Gynecol 206(4):300, 2012 Best E, Tennant PWG, Addor M, et al: Epidemiology of small intestinal atresia in Europe: a register-based study. Arch Dis Child Fetal Neonatal Ed 97(5):F353,e2012


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Obstentrics_Williams. Best E, Tennant PWG, Addor M, et al: Epidemiology of small intestinal atresia in Europe: a register-based study. Arch Dis Child Fetal Neonatal Ed 97(5):F353,e2012 Bhide A, Acharya G, Bilardo CM, et al: ISUOG Practice Guidelines: use of Doppier ultrasonography in obstetrics. Ultrasound Obstet Gynecol41 (2):233, 2013 Bilardo CM, Wolf H, Stigter RH, et al: Relationship between monitoring parameters and perinatal outcome in severe, early intrauterine growth restriction. Ultrasound Obstet Gynecol 23: 119, 2004 Bonafe L, Cormier-Daire V, Hall C, et al: Nosology and classification of genetic skeletal disorders: 2015 revision. Am J Med Genet 167A(12):2869, 2015 Bromley B, Shipp TO, Lyons J, et al: Detection of fetal structural anomalies in a basic first-trimester screening program for aneuploidy. J Ultrasound Med 33(10):1737,e2014


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Obstentrics_Williams. Bromley B, Shipp TO, Lyons J, et al: Detection of fetal structural anomalies in a basic first-trimester screening program for aneuploidy. J Ultrasound Med 33(10):1737,e2014 Bronshtein M, Ornoy A: Acrania: anencephaly resulting from secondary degeneration of a closed neural tube: two cases in the same family. J Clin Ultrasound 19(4):230, 1991 Brugger PC, Stuhr F, Lindner C, et al: Methods of fetal MR: beyond T2-weighted imaging. Euro J Radiol 57(2): 172, 2006 Burge 0, Wheeler R: Increasing incidence of detection of congenital lung lesions. Pediatr Pulmono1e45(1):103, 2010 Caire JT, Ramus RM, Magee KP, et al: MRI of fetal genitourinary anomalies. AJR Am J RoentgenoIe181:1381, 2003 Canield A, Honein A, Yuskiv N, et al: National estimates and race/ethnicspecific variation of selected birth defects in the United States, 1999-2001. Birth Defects Res A Clin Mol Teratol 76(11):747, 2006


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Obstentrics_Williams. Carey M, Bower C, Mylvaganam A, et al: Talipes equinovarus in Western Australia. Paediatr Perinat Epidemiol 17: 187, 2003 Cavoretto P, Molina F, Poggi S, et al: Prenatal diagnosis and outcome of echogenic fetal lung lesions. Ultrasound Obstet Gynecol 32:769, 2008 Centers for Disease Control and Prevention: Workplace solutions. Preventing work-related musculoskeletal disorders in sonography. DHHS (NIOSH) Publication No. 2006-148, 2006 Chitty LS, Altman DG: Charts of fetal size: kidney and renal pelvis measurements. Prenat Diagn 23:891, 2003 Christensen N, Andersen H, Garne E, et al: Atrioventricular septal defects among infants in Europe: a population-based study of prevalence, associated anomalies, and survival. Cardiol Young 23(4):560,e2013 Clements H, Duncan KR, Fielding K, et al: Infants exposed to MRI in utero have a normal paediatric assessment at 9 months of age. B J Radiol 73(866):190,e2000


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Obstentrics_Williams. Clements H, Duncan KR, Fielding K, et al: Infants exposed to MRI in utero have a normal paediatric assessment at 9 months of age. B J Radiol 73(866):190,e2000 Colvin J, Bower C, Dickinson JE, et al: Outcomes of congenital diaphragmatic hernia: a population-based study in Western Australia. Pediatr 116:e356, 2005 Copel JA, Liang R, Demasio K, et al: he clinical significance of the irregular fetal heart rhythm. Am J Obstet Gynecol 182:813,e2000 Cragan JD, Gilboa SM: Including prenatal diagnoses in birth defects monitoring: experience of the Metropolitan Atlanta Congenital Defects Program. Birth Defects Res A Clin Mol Teratol 85:20, 2009 Cruz-Martinez R, Figueras F, Hernandez-Andrade E, et al: Fetal brain Doppler to predict cesarean delivery for nonreassuring fetal status in term small-forgestational-age fetuses. Obstet Gynecol 117:618, 2011 Curran PF, Jelin EB, Rand L, et al: Prenatal steroids for microcystic congenital adenomatoid malformations. J Pediatr Surg 45:145,e2010


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Obstentrics_Williams. Curran PF, Jelin EB, Rand L, et al: Prenatal steroids for microcystic congenital adenomatoid malformations. J Pediatr Surg 45:145,e2010 Dashe JS, Mcintire DO, Twickler OM: Efect of maternal obesity on the ultrasound detection of anomalous fetuses. Obstet Gynecol 113(5):1001,o2009 De Biasio P, Ginocchio G, Aicardi G, et al: Ossification timing of sacral vertebrae by ultrasound in the mid-second trimester of pregnancy. Prenat Diagn 23:1056,o2003 Debus A, Hagelstein C, Kilian A, et al: Fetal lung volume in congenital diaphragmatic hernia: association of prenatal MR imaging indings with postnatal chronic lung disease. Radiology 266(3):887,o2013 Derikx JP, De Backer A, Van De Schoot L, et al: Factors associated with recurrence and metastasis in sacrococcygeal teratoma. Br J Surg 93: 1543, 2006 Devaseelan P, Cardwell C, Bell B, et al: Prognosis of isolated mild to moderate fetal cerebral ventriculomegly: a systematic review. J Perinat Med 38:401, 20o10


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Obstentrics_Williams. Devaseelan P, Cardwell C, Bell B, et al: Prognosis of isolated mild to moderate fetal cerebral ventriculomegly: a systematic review. J Perinat Med 38:401, 20o10 De Veciana M, Major CA, Porto M: Prediction of an abnormal karyotype in fetuses with omphalocele. Prenat Diagn 14:487, 1994 DeVore GR, Falkensammer P, Sklansky MS, et al: Spatio-temporal image correlation (STIC): new technology for evaluation of the fetal heart. Ultrasound Obstet Gynecol 22:380, 2003 Dolk H, Loane M, Garne E: The prevalence of congenital anomalies in Europe. Adv Exp Med Bioi 686:349, 2010 Duncombe GJ, DickinsonoJE, Kikiros CS: Prenatal diagnosis and management of congenital cystic adenomatoid malformation of the lung. Am J Obstet Gynecol 187(4): 950, 2002 Ecker JL, Shipp TO, Bromley B, et al: The sonographic diagnosis of DandyWalker and Dandy-Walker variant: associated indings and outcomes. Prenat Diagn 20:328, 2000


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Obstentrics_Williams. Ecker JL, Shipp TO, Bromley B, et al: The sonographic diagnosis of DandyWalker and Dandy-Walker variant: associated indings and outcomes. Prenat Diagn 20:328, 2000 EUROCAT: Prenatal Detection Rates. Available at: http://ww.eurocatnetwo rk. eu/ p rena talscreen inganddiagnosis/ p rena taldetectio n (pd) ra tes. Accessed July 10, 2017 Farhataziz N, Engels JE, Ramus RM, et al: Fetal MRI of urine and meconium by gestational age for the diagnosis of genitourinary and gastrointestinal abnormalities. AJR Am J Roentgenol 184: 1891, 2005 Feinstein JA, Benson OW, Dubin M, et al: Hypoplastic let heart syndrome: current considerations and expectations. J Am ColI Cardiol 59(1 Suppl):SI, 2012 Figueras F, Benavides A, Del Rio M, et al: Monitoring of fetuses with intrauterine growth restriction: longitudinal changes in ductus venosus and aortic isthmus flow. Ultrasound Obstet Gynecol 33(1):39, 2009


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Obstentrics_Williams. Food and Drug Administration: Avoid fetal "keepsake" images, heartbeat monitors. 2014. Available at: https://www.fda.gov/ForConsumers/ ConsumerUpdates/ucm095508.htm. Accessed July 10, 2017 Franklin 0, Burch M, Manning N, et al: Prenatal diagnosis of coarctation of the aorta improves survival and reduces morbidity. Heart 87:67, 2002 Furey A, Bailey A, Twickler OM: Fetal MR imaging of gastrointestinal abnormalities. Radiographies 36(3):904, 2016 Gaglioti P, Oberto M, Todros T: he signiicance of fetal ventriculomegaly: etiology, short-and long-term outcomes. Prenat Diagn 29(4):381, 2009 Gallot 0, Boda e, Ughetto S, et al: Prenatal detection and outcome of congenital diaphragmatic hernia: a French registry-based study. Ultrasound Obstet Gynecol 29:276, 2007 Garcia M, Yeo L, Romero R, et al: Prospective evaluation of the fetal heart using Fetal Intelligent Navigation Echocardiography (FINE)o. Ultrasound Obstet GynecoIo47(4):450, 2016


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Obstentrics_Williams. Goldstein I, Reece EA, Pilu G, et al: Cerebellar measurements with ultrasonography in the evaluation of fetal growth and development. Am J Obstet GynecoIo156:1065,o1987 Goncalves LF, Lee W, Espinoza J, et al: Three-and 4-dimensional ultrasound in obstetric practice: does it help? J Ultrasound Med 24: 1599, 2005 Goncalves LF, Nien JK, Espinoza J, et al: What does 2-dimensional imaging add to 3-and 4-dimensional obstetric ultrasonography? J Ultrasound Med 25:691,o2006 Griiths PO, Bradburn M, Campbell MJ, et al: Use ofMRI in the diagnosis of fetal brain abnormlities in utero (MERIDIAN): a multicenter, prospective cohort study. Lancet 389(10068):538, 2017 Gucciardo L, Uyttebroek A, de Wever I, et al: Prenatal assessment and management of sacrococcygeal teratoma. Prenat Diagn 31 :678, 2011 Hains OS, Bates CM, Ingraham S, et al: Management and etiology of the unilateral multicystic dysplastic kidney: a review. Pediatr NephroIo24:233, 2009


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Obstentrics_Williams. Yamada 5, Uwabe C, Fujii 5, et al: Phenotypic variability in human embryonic holoprosencephaly in the Kyoto collection. Birth Defects Res Part A Clin Mol TeratoIo70:495,o2004 Yeo L, Romero R: How to acquire cardiac volumes for sonographic examination of the fetal heart, part I. J Ultrasound Med 35 (5): 1 021, 2016 Yildirim G, Gungorduk K, Asian H, et al: Prenatal diagnosis of extralobar pulmonary sequestration. Arch Gynecol Obstet 278: 181, 2008 Zaretsky M, Ramus R, McIntire 0, et al: MRI calculation of lung volumes to predict outcome in fetuses with genitourinary abnormalities. AJR Am J RoentgenoIo185:1328,o2005 Zaretsky MV, McIntire DO, Twickler DM: Feasibility of the fetal anatomic and maternal pelvic survey by magnetic resonance imaging at term. Am J Obstet Gynecol 189:997, 2003a Zaretsky MY, Twickler OM: Magnetic imaging in obstetrics. Clin Obstet Gynecol 46:868, 2003b


Obstentrics_Williams

Obstentrics_Williams. Zaretsky MY, Twickler OM: Magnetic imaging in obstetrics. Clin Obstet Gynecol 46:868, 2003b Zeeman GG, McIntire DO, Twickler DM: Maternal and fetal artery Doppler findings in women with chronic hypertension who subsequently develop superimposed pre-eclampsia. J Matern Fetal Neonatal Med 14:318,o2003 Zerres K, Mucher G, Becker J, et al: Prenatal diagnosis of autosomal recessive polycystic kidney disease: molecular genetics, clinical experience, and fetal morphology. Am J Med Genet 6:l37, 1998 NORMAL AMNIONIC FLUID VOLUME .......... .....225 PHYSIOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 225 SONOGRAPHIC ASSESSMENT . .......... . .i..226 HYDRAMNIOS ......... ...i...i..i......... .....227 OLIGOHYDRAMNIOS ..i........ .... ....... .....230 BORDERLINE OLIGOHYDRAMNIOS ........... ...i.. 232


Obstentrics_Williams

Obstentrics_Williams. HYDRAMNIOS ......... ...i...i..i......... .....227 OLIGOHYDRAMNIOS ..i........ .... ....... .....230 BORDERLINE OLIGOHYDRAMNIOS ........... ...i.. 232 It is generaly agreed that amniotic luid represents in great part a transudation from the matenal vesses, but many authorities consider that a portion of it is derived rom urinay secretion of the oetus. -J. Whitridge Williams (1903)


Obstentrics_Williams

Obstentrics_Williams. -J. Whitridge Williams (1903) At the time Williams wrote this, the fetal kidney was thought by many to be nonfunctional. Since that time, however, much has been learned of this complex multifunctional liquor amnii. mnionic fluid serves several roles during pregnancy. Fetal breathing of amnionic fluid is essential for normal lung growth, and fetal swallowing permits gastrointestinal (GI) tract development. Amnionic fluid also creates a physical space for fetal movement, which is necessary for neuromusculoskeletal maturation. It further guards against umbilical cord compression and protects the fetus from trauma. Amnionic luid even has bacteriostatic properties. Abnormalities of volume may result from fetal or placental pathology-indicating a problem with luid production or its circulation. These volume extremes may be associated with increased risks for adverse pregnancy outcome.


Obstentrics_Williams

Obstentrics_Williams. Amnionic luid volume increases from approximately 30 mL at 10 weeks to 200 mL by 16 weeks and reaches 800 mL by the mid-third trimester (Brace, 1989; Magann, 1997). The luid is approximately 98-percent water. A full-term fetus contains roughly 2800 mL of water and the placenta another 400 mL, such that the term uterus holds nearly 4 liters of water (Modena, 2004). Abnormally decreased luid volume is termed oligohydramnios, whereas abnormally increased luid volume is termed hydramnios or poyhydramnios.


Obstentrics_Williams

Obstentrics_Williams. Early in pregnancy, the amnionic cavity is filled with luid that is similar in composition to extracellular luid. During the first half of pregnancy, transfer of water and other small molecules takes place across the amnion-transmembranous low; across the fetal vessels on placental surface-intramembranous low; and transcutaneous low-across fetal skin. Fetal urine production begins between 8 and 11 weeks' gestation, but it does not become a major component of amnionic luid until the second trimester, which explains why fetuses with lethal renal abnormalities may not manifest severe oligohydramnios until after 18 weeks. Water transport across the fetal skin continues until keratinization occurs at 22 to 25 weeks. This explains why extremely preterm neonates can experience signiicant luid loss across their skin. With advancing gestation, four pathways playia major role in amnionic luid volume regulation (Table