Is indication for induction of labor associated with mode of delivery in term first births? A Norwegian registry-based study.

Abstract

Introduction: Few previous studies have examined the association between the indication for induction of labor (IOL) and the mode of delivery. To improve information for clinicians and women undergoing IOL, our study aimed to assess the association between the indication for IOL and the risk of cesarean and operative vaginal birth among nulliparous women with single cephalic term pregnancies. Furthermore, we examined whether associations varied by gestational length. Lastly, we evaluated reasons for cesarean and operative vaginal birth across indications for IOL.

Material and methods: Data were extracted from the Medical Birth Registry of Norway from 2020 to 2021. We used the registered main indication for IOL. Multinomial logistic regression was applied to estimate relative risk ratios (RRRs) with associated 95% confidence intervals (CIs) of cesarean and operative vaginal birth versus spontaneous vaginal birth for the different IOL indications, using prelabor rupture of membranes (PROM) as the reference indication.

Results: Risk of cesarean versus spontaneous vaginal birth was four times higher for women induced due to large fetus compared to women induced due to PROM (adjusted RRR: 4.39; 95% CI: 3.21 to 5.99). Indications such as maternal request, post-term pregnancy, oligo-/polyhydramnios, preeclampsia/hypertension, and diabetes were associated with a 40%-91% increased relative risk of cesarean versus spontaneous vaginal birth compared to PROM. Relative risk of operative vaginal versus spontaneous vaginal birth was increased by 23%-29% for oligo-/polyhydramnios, diabetes, and post-term pregnancy compared to PROM. Indication large fetus had similar relative risk ratios at all gestational lengths. Rate of operative delivery for fetal distress was highest for IOL due to intrauterine growth restriction (IUGR). For secondary outcomes, IOL due to IUGR had the highest proportions of cesarean and operative vaginal birth for fetal distress. Indication post-term pregnancy had the highest proportion of cesarean birth for prolonged labor, while large fetus had the highest proportion of operative vaginal birth for prolonged labor.

Conclusions: Nulliparous women undergoing IOL for indications such as large fetus, post-term pregnancy, oligo-/polyhydramnios, preeclampsia/hypertension, and diabetes are at an elevated relative risk of cesarean versus spontaneous vaginal birth compared to IOL for PROM. In contrast, the relative risk of operative vaginal birth showed less variation by indication for IOL.