BMI-Stratified Risk of Cesarean Delivery Following Labor Induction: A Robson Classification-Based Cohort Study with Predictive Modeling.

Objectives: Maternal obesity is associated with adverse labor induction outcomes, but real-world data stratified by the full WHO body mass index (BMI) classification and adjusted for parity remain limited. We evaluated BMI-stratified induction outcomes using the Robson Ten-Group Classification System and developed a combined multivariable model integrating BMI, Bishop score, and parity for pre-induction risk stratification. Methods: This single-center retrospective cohort study included 501 singleton term pregnancies undergoing labor induction in Ankara, Turkey (March-August 2023), stratified by five WHO BMI categories. The primary outcome was cesarean delivery. Analyses included Cochran-Armitage trend tests, multivariable logistic regression, and ROC analysis with DeLong comparison and bootstrap optimism-corrected internal validation. The study followed STROBE guidelines. Results: The overall cesarean rate was 30.3%, rising from 17.1% (normal weight) to 52.2% (Obese class III; Cochran-Armitage Z = 6.099, p < 0.001), with consistent trends across Robson Groups 2 and 4 (both p < 0.001). Failed induction increased from 2.9% to 15.2% (p < 0.001). The cervical ripening requirement rose from 32.4% to 60.9% (p = 0.003). BMI (adjusted odds ratio [aOR] = 1.489, 95% confidence interval [CI] 1.254-1.767) and Bishop score (aOR = 0.807, 95% CI 0.718-0.906) were independent predictors; nulliparity showed a non-significant trend (p = 0.090). The combined model (BMI + Bishop + nulliparity) achieved an apparent AUC of 0.715 (optimism-corrected 0.709), outperforming both Bishop score alone (DeLong p = 0.010) and BMI alone (p = 0.012). Calibration was adequate (Hosmer-Lemeshow p = 0.632). Conclusions: Higher BMI independently predicts increased cesarean risk following labor induction across parity subgroups. The combined multivariable model provides practical bedside pre-induction risk stratification superior to either individual predictor, though external validation is warranted before widespread clinical implementation.