Does a larger estimated fetus compared with prior birthweight increase the risk of cesarean delivery after a prior vaginal birth?

Purpose To evaluate whether an increase in estimated fetal weight (EFW) relative to the birthweight of a prior vaginal delivery is associated with intrapartum cesarean delivery (CD) or other adverse obstetric outcomes. Methods This retrospective cohort study included patients with two consecutive term singleton deliveries (2014–2025). All had a vaginal first delivery and underwent a trial of labor in the second pregnancy. Patients were categorized by the difference between EFW and prior birthweight: higher (> 15%) and similar (-15% to 15%). The primary outcome was intrapartum CD. Multivariable logistic regression adjusted for clinically relevant confounders. Subgroup analysis stratified by EFW (< 3500 vs. ≥ 3500 g) evaluated the effect of absolute fetal size. Results The primary analysis included 2849 patients: 2265 in the similar-weight group and 584 in the higher-weight group. The crude intrapartum CD rate was higher in the higher-weight group (5.3% vs 3.0%, p = 0.006). After adjustment, weight difference was not independently associated with CD (adjusted odds ratio [aOR] 1.43; 95% CI 0.91–2.27; p = 0.12). In subgroup analysis, among patients with EFW ≥ 3500 g, a trend toward increased CD risk was observed in the higher-weight group (aOR 1.68, 95% CI 0.94–2.99, p = 0.08). Conclusion An increase in EFW relative to prior birthweight was not independently associated with intrapartum CD among patients with a prior vaginal delivery. Among patients with larger absolute EFW, a non-significant trend toward increased intrapartum CD risk was observed, a finding that warrants future investigation. These findings suggest that interpregnancy weight differences alone should not guide delivery planning in otherwise uncomplicated pregnancies.