(839) Influence of gestational age and maternal obesity on cesarean delivery rates in term inductions

Objective:
To compare the rate of cesarean delivery (CD) in low-risk nulliparous women undergoing induction of labor (IOL) at different gestational ages and across BMI groups.

Study Design:
This is a secondary, post hoc subgroup analysis of a multicenter randomized controlled trial of IOL at 39 weeks compared with expectant management in low-risk nulliparous women (ARRIVE). Only participants who were admitted for IOL were included, irrespective of their group allocation in the parent study. Primary outcome was rate of CD. Secondary outcomes were maternal (duration from admission to delivery, operative vaginal delivery, OASIS, preeclampsia or gestational hypertension, chorioamnionitis, postpartum hemorrhage, postpartum infection, shoulder dystocia) and neonatal (birthweight, macrosomia, a composite of adverse outcomes). Modified Poisson and log-linear regressions were performed to estimate adjusted relative risks; Chi-square and Mann-Whitney U tests were used for group comparisons.

Results:
3547 patients were included: 215 were induced at 38 weeks, 2551 at 39 weeks, and 781 at ≥40 weeks. The goup induced at 39 weeks was reference. Baseline demographics were similar, except for advanced maternal age (39 v 40), private insurance (39 v 38), tobacco use (39 v 40), previous pregnancy loss (39 v 40), and PROM (39 v 38 and 39 v 40). After adjustment for significant variables, rate of CD was significantly higher in those induced at ≥40 weeks than those induced at 39 weeks (33.7% v 20.9%, respectively, 95% CI 1.59 [1.40-1.80]), irrespective of BMI category (Figure). No significant difference in this rate was noted for IOL at 38 weeks. Furthermore, the rates of any of the secondary maternal and neonatal outcomes were not significantly different between those induced at 39 weeks versus 38 weeks or ≥40 weeks (Table).

Conclusion:
IOL at ≥40 weeks is associated with a significantly higher cesarean rate across all BMI strata, most pronounced in BMI ≥40, without difference in neonatal outcomes.