spontaneous labor

Also found in: Dictionary, Thesaurus, Legal, Encyclopedia.
Related to spontaneous labor: parturition


the physiologic process by which the uterus expels the products of conception (fetus or newborn and placenta), after 20 or more weeks of gestation. It may be divided into three stages: The first stage (dilatation) begins with the onset of regular uterine contractions and ends when the cervical os is completely dilated and flush with the vagina, thus completing the birth canal. The second stage (expulsion) extends from the end of the first stage until the expulsion of the infant is completed. The third stage (placental stage) extends from the expulsion of the child until the placenta and membrane are expelled and contraction of the uterus is completed. Called also accouchement and parturition.

Labor is believed to be triggered by the release of oxytocin and prostaglandins, after a fall in the levels of other hormones. Normally at the end of pregnancy oxytocin, which is stored in the posterior lobe of the pituitary gland, is released and stimulates contraction of the uterine muscles.

The progress and final outcome of labor are influenced by four factors: (1) the “passage” (the soft and bony tissues of the maternal pelvis); (2) the “powers” (the contractions or forces of the uterus); (3) the “passenger” (the fetus); and (4) the “psyche” (mother's emotional state, e.g., anxiety).

The mechanisms of labor (for a vertex presentation) consist of the following sequence of events: engagement (posterior occiput of fetus enters the pelvic outlet); flexion (of fetal head); descent (fetal head descends lower into the midpelvis); internal rotation (fetal head and body rotate so that the occiput is more anterior); extension (fetal head extends once the occiput is beneath the symphysis pubis); and external rotation (fetal head rotates back to position it had at engagement).
First Stage of Labor. The beginning of labor is usually indicated by one or more of the following signs: (1) show (passage from the vagina of small quantities of blood-tinged mucus); (2) breaking the “bag of waters” (normal rupture of membranes, indicated by a gush or slow leakage of amniotic fluid from the vagina); and (3) true labor contractions. The first two of these signs are almost always unmistakable. The contractions, however, can be confusing. braxton-hicks contractions, or “false labor pains,” can be distinguished from true labor contractions by the irregular time intervals between them and by their tendency to disappear when the patient changes position or gets up and walks about. True labor contractions are regularly spaced and usually start in the small of the back, or as a feeling of tightness in the abdomen, or of pressure in the pelvis. The contractions recur at shorter and shorter intervals, every three to five minutes, and become progressively stronger and longer lasting. The increase in the strength of contractions usually is accompanied by an increase in the amount of show because of rupture of capillaries in the dilating cervix.

This first stage of childbirth is known as the dilatation period. The uterus is like a large rubber bottle with a half-inch long neck that is almost closed. As the uterine muscles contract, the cervix becomes thinner (effacement) and more open (dilated) so that the neck of the uterus eventually resembles that of a jar more than that of a bottle.

The length of the first stage of labor varies with each individual patient, with an average of 8 to 12 hours in primiparous and 6 to 8 hours in multiparous women. It is related to the strength and effectiveness of the contractions and is a period when the mother is instructed to relax as much as possible and let the uterus do the work. Pushing or bearing down is not effective during this stage and is harmful in that it may cause a tearing of the cervix and will only serve to exhaust the woman. She is encouraged to rest and possibly to nap between contractions.

The second stage of labor may be heralded by symptoms of nausea, vomiting, irritability, the urge to bear down, or periods of feeling hot and then cold, signs of the period of transition from the first to the second stage.
Second Stage of Labor. This period, called the expulsion stage, usually is characterized by intense contractions that last for about one full minute and occur at 2 to 3 minute intervals. The cervix is fully dilated and the woman is able to help with this process by bearing down with each uterine contraction, using her abdominal muscles to help expel the infant. This stage varies from a few minutes to one to two hours.
Third Stage of Labor. In this stage the placenta detaches itself from the uterine wall and is expelled. The process takes about 15 minutes, and is painless.
Fourth Stage of Labor. This final stage is the stage of recovery and lasts 2 to 4 hours.
Patient Care. Once labor has begun the patient should have someone in constant attendance. She will derive much emotional support from one who is warm, kind, and understanding, and displays a genuine interest in her welfare and that of her infant. It is best to have the same person care for her through the entire labor and birth process.

During labor the strength, frequency, and duration of contractions are noted and recorded. It is expected that the contractions will increase in all three characteristics, but a sudden change in any one should be reported to the health care provider immediately. The rate, regularity, and volume of the fetal heart tones are checked and recorded periodically. Some apprehensive patients may be helped by allowing them to listen to the infant's heartbeat.

Food and fluids are withheld during active labor, but thirst may cause some discomfort and may be lessened by allowing the patient to moisten her lips with a gauze sponge or to suck on ice chips. Intravenous fluids are usually given. Frequent bathing of the face with a cool washcloth often helps relieve the flushed feeling brought about by the actual hard work being done by the mother. Frequent changing of her gown and of the pad protecting the bed linens may be necessary to keep her clean, dry, and comfortable.

If there is a support person with the woman during labor, that person should be instructed in ways he or she can help the patient and at the same time feel that he or she is making some contribution in this very important event. The support person may wish to participate in keeping a record of the contractions, or might appreciate the opportunity to listen to the fetal heart tones occasionally. If the patient feels that sacral support during each contraction helps mitigate the pain, the support person can be shown how to do this. Some supporters have attended classes for expectant parents and are prepared for their role during labor and delivery. Both the patient and the support person should be informed of the progress during labor so they can feel that something is being accomplished by their efforts.

The patient is encouraged to rest and relax between contractions so as to conserve her strength. She should not bear down until the cervix is fully dilated, since this effort will only serve to exhaust her and may cause lacerations of the cervix. After the cervix is fully dilated she can speed the birth process by holding her breath and contracting her abdominal muscles. Controlled breathing exercises learned in classes for expectant parents promote relaxation and aid labor.

Although serious complications rarely develop during labor, they can occur and must be watched for. Observations to report immediately include hyperactivity of the fetus; vaginal bleeding in excess of a heavy show; a rapid and irregular pulse and drop in blood pressure; sudden rise in blood pressure; and headache, visual disturbances, extreme restlessness, or rapidly developing edema. A sudden cessation of contractions or a contraction that does not relax may indicate a serious disturbance in the labor process. The appearance of meconium in the vaginal discharge may indicate fetal distress unless the infant is in a breech position. (See also fetal monitoring.)
Schematic representation of factors believed to have a role in starting labor. From Gorrie et al., 1994.
artificial labor induced labor.
dry labor a lay term indicating that in which the amniotic fluid escapes before contraction of the uterus begins.
false labor false pains.
induced labor that which is brought on by extraneous means, e.g., by the use of drugs that cause uterine contractions; called also artificial labor.
instrumental labor delivery facilitated by the use of instruments, particularly forceps.
missed labor that in which contractions begin and then cease, the fetus being retained for weeks or months.
precipitate labor delivery accomplished with undue speed.
premature labor expulsion of a viable infant before the normal end of gestation; usually applied to interruption of pregnancy between the twenty-eighth and thirty-seventh weeks.
preterm labor labor commencing before the end of 37 completed weeks of gestation; it can be arrested (see tocolysis) and does not necessarily lead to preterm delivery. Preterm labor can be treated by bed rest at home and use of a tokodynamometer with a recording unit that transmits data about uterine activity over the telephone to a monitoring station. Tocolytic drugs, including ritodrine hydrochloride and terbutaline, may be used to relax the uterine muscles.
spontaneous labor delivery occurring without artificial aid.

spontaneous labor

Labor that begins and progresses without pharmacological, mechanical, or operative intervention.
See also: labor
Medical Dictionary, © 2009 Farlex and Partners
References in periodicals archive ?
Before analgesia, the oxytocin augmented group had a pain score of 7.9, while the spontaneous labor group had a score of 8.2.
According to the latest American college of obstetricians and gynecologists American College of Obstetricians and Gynaecologist (ACOG) guidelines, in spontaneous labor as long as fetomaternal status are reassuring, arrest of labor in first stage is defined as more than or equal to 6cm cervical dilatation with membrane rupture and 4 hours or more of adequate contraction or 6 hours or more of inadequate contraction and no cervical change.
Despite postoperative administration of tocolytic agents, including ritodrine hydrochloride and magnesium sulphate, spontaneous labor pain occurred, resulting in extremely preterm birth at 23 weeks, 3 days of gestation.
On analysis of indications of CS in primigravida group with spontaneous labor (Group 1), 59 CS were performed out of 96, following non-reassuring cardiotocogram (CTG).
Comparative analysis of international cesarean delivery rates using 10-group classification identifies significant variation in spontaneous labor. Am J Obstet Gynecol 2009; 201: 308 e1-8.
"Women who are induced in the 37th to 38th week have a significantly higher risk of having a cesarean section than mothers who have spontaneous labor," according to the Leapfrog Group.
Latin American women with low-risk pregnancies who undergo elective labor induction are at increased risk for adverse maternal and perinatal outcomes, compared with those who experience spontaneous labor, according to an eight-country study.
She presented in spontaneous labor at 38 6/7 weeks gestation and had a spontaneous delivery of a healthy 7 pound, 13 oz female infant with a third degree midline laceration.
Thus, preparations for labor start at about 8 to 12 days prior to the onset of spontaneous labor as indicated by AFOD surge and its duration.
Induction of labor is defined as the stimulation of uterine contractions to cause the delivery of an infant before spontaneous labor occurs (Kirby, 2004).
-- Epidural analgesia given in early labor has been shown to have no significant effect on the risk of operative delivery in patients with spontaneous labor, and the same appears to hold true for patients with induced labor, according to data presented at the annual meeting of the Society for Obstetric Anesthesia and Perinatology.

Full browser ?