Cumulative risk score predicts VBAC success and NICU admission in 477,693 TOLAC attempts.

This national validation study analyzed data from Centers for Disease Control and Prevention natality files involving 477,693 term, singleton deliveries with trial of labor after cesarean (TOLAC) between 2020 and 2024. The exposure was a cumulative risk score ranging from -1 to 7 points, which incorporated maternal BMI, induction of labor, diabetes mellitus, hypertensive disorder, maternal age, gestational age, and prior vaginal delivery. The primary outcome was VBAC success, with secondary outcomes including neonatal intensive care unit (NICU) admission rates.

Results demonstrated a monotonic relationship between the cumulative risk score and VBAC success. Success rates decreased as the score increased: 90.5% for a score of -1, 76.4% for 0, 69.4% for 1, 62.2% for 2, 55% for 3, and 44.8% for a score of 4 or higher. Overall, 350,340 of 477,693 attempts (73.3%) resulted in successful VBAC. Prior vaginal delivery emerged as the strongest individual predictor, associated with an 86.4% success rate compared to 62.5% for those without a prior vaginal delivery.

NICU admission rates increased concordantly across risk strata, ranging from 43.8 to 111.1 per 1,000 deliveries. The study observed stable TOLAC volumes across the follow-up period. No specific adverse events or discontinuations were reported beyond the secondary outcome of NICU admission. The cumulative risk score demonstrated a monotonic relationship with both VBAC success and NICU admission rates.

Key limitations regarding study design or specific confounding adjustments were not reported in the provided data. As an observational cohort study, these findings describe associations rather than causation. The practice relevance supports using this score for individualized TOLAC counseling, acknowledging that risk stratification must be interpreted within the context of the specific patient population and clinical setting.