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Am Fam Physician. 2001;63(4):739-740

Optimal management of pregnancies that extend beyond 40 weeks of gestation presents a clinical dilemma. The American College of Obstetricians and Gynecologists currently recommends that labor be induced at 42 weeks of gestation in women with favorable cervices, while fetal surveillance is indicated in women whose cervices are unlikely to respond to ripening. The dilemma concerns the risks to the fetus from extended pregnancy versus the risks associated with a more complicated delivery if labor is induced. Alexander and colleagues assessed pregnancy outcomes following induction at 40, 41 and 42 weeks of gestation to identify the risks and benefits of routine labor induction in “postdate” pregnancies.

More than 82,000 women who delivered at or after 40 weeks of gestation at a large public hospital in Texas during 1998 were eligible for the study. Women with hypertension, diabetes, previous Cesarean births, fetal malformations, breech presentations and placenta previa were excluded. Gestational age was estimated by obstetricians on the basis of the date of the last menstrual period and available ultrasound evidence. Gestational age was estimated by pediatricians on delivery, and it concurred with the obstetric estimates in 90 percent of cases. Labor induction was initiated for maternal or fetal indications, or both, according to standardized protocols.

Data from a total of 29,136 deliveries at 40 weeks, 16,386 deliveries at 41 weeks and 10,795 deliveries at 42 weeks of gestation were analyzed for the study. Nulliparous women were statistically over-represented in those delivering at 41 and 42 weeks. The proportion of Hispanic mothers was also higher in these later delivery stages. Complications of labor increased progressively with weeks of gestation. The use of oxytocin during induction increased from 2 percent to 35 percent, the average duration of labor approximately doubled, use of forceps rose from 6 percent to 9 percent and Cesarean delivery rates doubled from 7 percent to 14 percent. Conversely, neonatal outcomes such as Apgar score, rate of admission to the intensive care unit, seizures, perinatal mortality and low umbilical artery pH values were comparable across groups. Birth weight increased significantly with increased gestation, and the proportion of infants born weighing more than 4,000 g (8 lb, 11 oz) rose significantly, from 8 percent to 15 percent. Sepsis was more common in infants delivered at 42 weeks of gestation than in those delivered at 40 or 41 weeks, but this was a rare event (0.3 percent compared with 0.1 percent). The number of stillbirths and neonatal deaths, respectively, were 45 and six at 40 weeks, 22 and four at 41 weeks, and 17 and six at 42 weeks.

The authors conclude that although complications of labor appeared to increase with extended gestation, infant outcomes were similar. They also emphasize that routine induction of labor at 41 weeks of gestation increases complications of labor with little or no benefit to the infant.

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Copyright © 2001 by the American Academy of Family Physicians.

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