Validation of a new calculator for predicting success of vaginal birth after cesarean delivery

Race as a variable in a predictive model for a successful vaginal birth after cesarean delivery has been challenged as contributing to health inequity. In May 2022, the National Institute of Child Health and Development released a modified calculator that removed race as a variable. The aim of this study was to externally validate the revised calculator amongst a cohort at our institution. We reviewed all patients who underwent a trial of labor after cesarean delivery in 2018-2020 at a tertiary academic medical center and calculated the predicted probability of successful vaginal birth after cesarean delivery for each patient using both original and revised classification calculators and compared these to observed birth outcomes. The area under the receiver operating characteristic curve was calculated for each model. From the cohort of 225 patients that fit inclusion criteria, 37% (n=83) identified as African-American or Hispanic. The vaginal birth after cesarean delivery success rate was 75% for the entire population, and 76% among African-American and/or Hispanic patients. The area under the receiver operating characteristic curve of the original calculator was 0.71, compared to 0.74 for the new calculator. For African-American and/or Hispanic patients, the average predicted success rates between the models rose from 60 to 69%. Our review confirmed that African-American and Hispanic patients were calculated to have a lower prediction score for a successful vaginal birth after cesarean delivery based on the original calculator as compared to the revised calculator. Our results also suggest that race/ethnicity did not significantly contribute to classification ability of the calculator in our patient population.