Association of maternal body mass index with success and outcomes of attempted operative vaginal delivery

BACKGROUND: Increasing maternal body mass index is associated with increased morbidity at cesarean delivery in a dose-dependent manner. In some clinical scenarios, operative vaginal delivery is a strategy to prevent the morbidity associated with second-stage cesarean delivery, but the relationship between maternal body mass index and outcomes of attempted operative vaginal delivery is not well characterized.OBJECTIVE: This study aimed to assess whether the success of and adverse outcomes after attempted operative vaginal delivery are associ-ated with maternal body mass index at delivery among nulliparous individuals.STUDY DESIGN: This was a secondary analysis from the prospective cohort Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-To-Be study. This analysis included cephalic live-born nonanomalous singleton pregnancies >34 weeks at delivery with an attempted operative vaginal delivery (either forceps or vacuum). The primary exposure was maternal body mass index at delivery (>30 vs <30 kg/m2 [referent]). The primary outcome was an unsuccessful operative vaginal delivery attempt, defined as a cesarean delivery after an attempted operative vaginal delivery. The secondary outcomes included maternal and neonatal adverse outcomes. Multivariable logistic regression was used, and statistical interaction between operative instrument type (vacuum vs forceps) and body mass index was assessed.RESULTS: Of 10,038 assessed individuals, 791 (7.9%) had an attempted operative vaginal delivery and were included in this analysis. Of note, 325 individuals (41%) had a body mass index >30 kg/m2 at deliv-ery. Overall, 42 of 791 participants (5%) experienced an unsuccessful operative vaginal delivery. Individuals with a body mass index >30 kg/m2 at delivery were more than twice as likely to have an unsuccessful operative vaginal delivery than those with a body mass index <30 kg/m2 (8.0% vs 3.4%; adjusted odds ratio, 2.23; 95% confidence interval, 1.16-4.28; P=.005). Composite maternal morbidity and composite neonatal morbidity did not vary by body mass index group. There was no evidence of interaction or effect modification by operative instrument type for the rate of unsuccessful operative vaginal delivery attempt, composite maternal morbidity, or composite neonatal morbidity.CONCLUSION: Among nulliparous individuals who underwent an attempted operative vaginal delivery, those with a body mass index >30 kg/m2 at delivery were more likely to have an unsuccessful operative vagi-nal delivery attempt than those with a body mass index <30 kg/m2. There was no difference in composite maternal or neonatal morbidity after attempted operative vaginal delivery by body mass index category.