National Validation of a Dual-Outcome Risk Score for Trial of Labor After Cesarean: A Population-Based Analysis of 477,693 Deliveries

Objective: To externally validate, at the national level, a cumulative risk score for vaginal birth after cesarean (VBAC) success and neonatal morbidity derived from single center data. Methods: We conducted a population based cohort study of all trial of labor after cesarean (TOLAC) attempts among term, singleton deliveries recorded in the Centers for Disease Control and Prevention natality files, 2020 to 2024 (N=477,693). The cumulative risk score (range - 1 to 7 points) incorporated body mass index (BMI) 30 or greater (+1), BMI 40 or greater (+1), induction of labor (IOL; +1), diabetes mellitus (+1), hypertensive disorder (+1), maternal age 40 years or older (+1), gestational age 41 weeks or greater (+1), and prior vaginal delivery (-1). VBAC success rates and neonatal intensive care unit (NICU) admission rates were evaluated across risk strata. Results: The overall VBAC rate was 73.3% (350,340/477,693). The cumulative risk score demonstrated a monotonic relationship with VBAC success: score -1, 90.5%; score 0, 76.4%; score 1, 69.4%; score 2, 62.2%; score 3, 55%; and score 4 or higher, 44.8%. NICU admission rates increased concordantly from 43.8 to 111.1 per 1,000 across strata. Prior vaginal delivery was the strongest individual predictor (VBAC 86.4% vs 62.5%). VBAC rates and TOLAC volume were stable across 2020 to 2024. Conclusion: The cumulative risk score derived from single center data was externally validated in a national cohort of 477,693 TOLAC attempts. The monotonic dose-response relationship between risk score and both VBAC success and NICU admission was confirmed, supporting the use of this score for individualized TOLAC counseling.