Prediction of Vaginal Delivery in Pregnant Individuals with Class III Obesity Undergoing Induction of Labor: Development and Internal Validation of a Prediction Model

Objective: The objective of this study was to develop and internally validate a model predicting vaginal delivery after labor induction in individuals with class III obesity, and to describe maternal and neonatal outcomes by delivery mode. Methods: This was a retrospective cohort study of singleton term inductions in individuals with class III obesity (BMI ≥ 40 kg/m2) and no prior cesarean delivery at a tertiary care center (2010–2020). Eight predictors available at admission for induction were prespecified: maternal age, parity, pre-pregnancy BMI, gestational weight gain, prior bariatric surgery, hypertensive disorders, diabetes mellitus, and cervical dilation. Missing data were addressed using multiple imputation. Internal validation was carried out using bootstrap resampling, and coefficients were shrunken using the optimism-corrected calibration slope. Results: Of 183 individuals, 92 (50.3%) achieved vaginal delivery. The mean BMI was 50.5 ± 5.2 kg/m2; 68.9% were nulliparous. Multiparity (adjusted odds ratio [aOR] 7.38, 95% CI 3.26–16.70) and younger maternal age (aOR 0.91 per year, 95% CI 0.85–0.98) were associated with vaginal delivery; BMI was not (aOR 0.99 per kg/m2, 95% CI 0.93–1.06). Labor dystocia accounted for 69 of 91 cesarean deliveries (75.8%). Composite maternal morbidity occurred in 9.8% of patients after vaginal delivery and in 14.3% after cesarean delivery. The optimism-corrected AUC was 0.746 (95% CI 0.675–0.806) and the optimism-corrected calibration slope was 0.74. Conclusion: Half of the individuals with class III obesity achieved vaginal delivery after labor induction. Parity, not BMI, was the main determinant. This internally validated model requires external validation before it is used for counseling.