Predictors of cesarean section following elective post-dates induction of labor in nullipara with uncomplicated singleton vertex pregnancies.

Objective: Although post-dates is among the most common indications for induction of labor, no studies have identified the predictors of cesarean section (C/S) in that population. The high cesarean rate in our institution for this group of women triggered us to assess different induction practices to elicit potential causes.

Methods: We conducted a hospital-based retrospective cohort analysis using chart reviews of all nullipara women with induced labor at the Children's and Women's Health Centre of British Columbia, Vancouver, Canada, during the 2-year period, April 1998 to March 2000. The C/S rate was compared among 3 groups of women who were divided according to their induction method.

Results: Three hundred and thirty-nine women meeting the inclusion criteria were induced. Of the 25 women who received oxytocin ideally and the 111 women who did not, 7 (28%) and 53 (48%) were delivered by C/S, (x2=3.228 p=0.07; relative risks 0.59 [95% confidence interval 0.30, 1.13]). A significantly lower C/S rate (x2=21.9, p<0.0005) was found among women induced with prostaglandin (PG) alone (19.4%) compared with those induced with PG and oxytocin, whether oxytocin was given ideally (38.3%) or not ideally (45.4%). Of women who received oxytocin, there was no difference in chorioamnionitis (x2=0.485, p=0.49) between those who had an early membrane rupture (with or pre-oxytocin, 22.4%) and those who had membrane rupture following a period of oxytocin infusion (18.5%).

Conclusion: The need for oxytocin or less than 2 doses of PG is associated with increased risk of C/S. Whether oxytocin was given according to protocol (ideally) or not, made no difference to the C/S risk in this population.