Prolonged pregnancy: induction of labor and cesarean births

To determine the effects of labor induction on cesarean delivery in post-date pregnancies.

A total of 1325 women who reached 41 weeks' gestation between December 1, 1997, and April 4, 2000, and who were scheduled for induction of labor at 42 weeks were included in this prospective observational study. Cesarean delivery rates were compared between those women who entered spontaneous labor and those who underwent induction. Women with any medical or obstetric risk factors were excluded. A power analysis was performed to determine how many patients would be required to show no effect of labor induction on cesarean delivery with a beta of.8 and an alpha of.05. Approximately 5200 patients would be required, taking an estimated 28 years to accrue at our institution.

Admission to delivery was longer (5.7 compared with 11.1 hours, P =.001) and more likely to extend beyond 10 hours (55 compared with 24%, P =.001) in the induction group. Cesarean deliveries were increased in the induced group (19 compared with 14%, P <.001) due to cesarean for failure to progress (14 compared with 8%, P <.001). Independent risk factors for cesarean delivery included nulliparity, undilated cervix prior to labor, and epidural analgesia. Correction for these risk factors using logistic regression analysis revealed that it was the risk factors, and not induction of labor per se, that increased cesarean delivery.

Risk factors intrinsic to the patient, rather than labor induction itself, are the cause of excess cesarean deliveries in women with prolonged pregnancies.