Women who have had a cesarean delivery and subsequently plan a vaginal delivery have an elevated risk of having an infant who is stillborn or dies within four weeks after birth, according to a retrospective cohort study conducted in Scotland.¹ Among singleton infants born to such women after an uncomplicated term pregnancy, the perinatal death rate is 12.9 per 10,000 births. The odds of perinatal death for this group are more than 11 times those associated with a planned repeat cesarean birth and more than twice those among infants born to other multiparous women who do not plan a cesarean delivery; however, the odds are similar to those among infants of nulliparous women who do not expect to deliver by this method.

Researchers studied outcomes of all births, as well as clinical and demographic characteristics of women who delivered, from January 1992 through December 1997 by analyzing linked data from two national databases. Of the singleton births, 313,238 met the following criteria: They occurred at 37-43 weeks' gestation, the fetus presented head-down, any stillbirth during labor or neonatal death was not due to congenital conditions and delivery was not by planned cesarean section unless there was a history of this birth method. Five percent of the mothers had had at least one prior cesarean delivery but did not plan a surgical delivery for the current pregnancy, 3% had previously had a cesarean section and intended to undergo this procedure again, 48% were multiparous and had no history of cesarean delivery, and 44% were nulliparous.

Among women who had had a cesarean section, those who did not schedule a repeat procedure had an average age of 30 and a median height of 161 cm; those who did so were significantly older (31) and shorter (159 cm). Nulliparous and other multiparous women, by contrast, were significantly younger (26-29) and taller (162-163 cm). There were some differences among the four groups of women in terms of smoking status; level of socioeconomic deprivation; proportion of infants who had low birth weight; and infant's gestational age at birth, median birth weight and five-minute Apgar score. These factors were corrected for in subsequent analyses.

The rate of perinatal death among infants born to women with a history of cesarean section who did not schedule a repeat procedure was 12.9 per 10,000 births; for infants born by planned repeat cesarean delivery, the rate was 1.1 per 10,000. Among infants born to women with no history of cesarean delivery, the rates were 5.9 and 9.8 per 10,000 births to multiparous and nulliparous women, respectively. The results were similar in analyses that included only births for which complete records were available and in analyses restricted to births that occurred at or after 40 weeks' gestation (to exclude any women who had planned a cesarean delivery at term but had undergone an emergency procedure before the scheduled date).

Logistic regression analysis revealed that the odds of perinatal death among infants born to women with a history of cesarean section who did not intend to deliver by this method were more than 11 times those among infants born by a scheduled repeat cesarean delivery (odds ratio, 11.6) and more than twice those among infants born to other multiparous women (2.2). However, the odds among infants born to women who had previously undergone a cesarean section but did not schedule a repeat procedure were not significantly different from those among infants of the nulliparous women studied. In analyses that included only births for which complete records were available, adjustment for maternal characteristics, gestational age at birth and birth weight had no effect on the odds ratios.

The most common causes of perinatal mortality among infants born to women who had had a cesarean section but expected a vaginal delivery were mechanical factors (uterine rupture, umbilical cord compression or prolapse, birth trauma and asphyxia) and oxygen deprivation during birth: The rate for each was 4.5 deaths per 10,000 births. The odds of neonatal death due to mechanical factors for this group of women were more than eight times those for both multiparous women with no history of cesarean birth and nulliparous women (odds ratios, 8.5 and 8.8, respectively); the odds of neonatal death due to oxygen deprivation were about three times those for the other multiparous women (2.8).

The investigators note that infants born to women by planned repeat cesarean delivery had the lowest risk of perinatal death among the four study groups. However, because only one such death was identified, multivariate comparisons were "problematic"; the researchers recommend that larger studies be conducted in the future. According to their estimates, at most one in 500 women who have a history of cesarean section and plan a vaginal birth will have an infant who is stillborn or dies soon after birth. The researchers state that their findings "provide essential information for [these] women to make an informed choice," especially given that obstetricians face "pressure from government and health care insurers to advocate vaginal birth after cesarean delivery as one strategy to reduce the overall rate of cesarean delivery."

--T. Lane

REFERENCE

1. Smith GCS et al., Risk of perinatal death associated with labor after previous cesarean delivery in uncomplicated term pregnancies, Journal of the American Medical Association, 2002, 287(20):2684-2690.