(682) Induction of labor at 39 Weeks and Cesarean delivery Rates: A Nulliparous Cohort Study

Nullipara with singleton pregnancies, cephalic presentation, who delivered from 39 WG+0d, within a French perinatal network, between January 1, 2017 and December 31, 2024, were included. Prelabor CD performed prior to 39 WG were excluded.
Monthly rates of induction at 39 WG, and CD rates were modelled over time. The association between induction of labor at 39 WG and CD was evaluated using a multivariate mixed-effects model (accounting for maternity centers), adjusted for maternal age ( >35 years), birth weight ( >4000 g), and year of delivery. A sensitivity analysis was conducted excluding spontaneous births at 39 WG.

Results:

A total of 34,143 nulliparous women were included. During the study period, the induction rate at 39 WG was 9.8% (3,342/34,143), with a significant yearly increase over time. (1,1%, 95%CI [0,8%-1,4%],p< 0,001. The overall CD rate was 20.9% (7,150/34,143), without significant temporal change (+0,1% per year, p=0,26). Induction at 39 WG, maternal age >35 years, and birth weight >4000 g were significantly associated with an increased CD risk: Adjusted OR (aOR) = 1.71 [1.57 – 1.85] for induction of labor, aOR = 1.70 [1.58 – 1.82] for maternal age >35 years, and aOR = 2.73 [2.48 – 3.00] for birth weight >4000 g. The sensitivity analysis yielded similar results.

 

Conclusion:

Induction rate at 39 WG increased during the study period and was significantly associated with an increased risk of CD. However, its low incidence did not significantly impact the overall CD in nulliparous women at 39 WG. The discrepancy between our results and previous publication are possibly explained by different organizational factors which may influence the CD risk and which require important future investigations.