Assessing the predictive accuracy of the new vaginal birth after cesarean delivery calculator

Background: The vaginal birth after cesarean delivery calculator by the Maternal-Fetal Medicine Units Network was created to help providers counsel patients on predicted success of trial of labor after cesarean delivery using individualized risk assessment. The inclusion of race and ethnicity as predictors of vaginal birth after cesarean delivery in the 2007 calculator was problematic and potentially exacerbated racial disparities in obstetrics. Thus, a modified calculator without race and ethnicity was published in June 2021.

Objective: This study aimed to assess the accuracy of the 2007 and 2021 Maternal-Fetal Medicine Units vaginal birth after cesarean delivery calculators in predicting vaginal birth after cesarean delivery success among racial/ethnic minority patients receiving obstetrical care at a single urban tertiary medical center.

Study design: All patients with 1 previous low transverse cesarean delivery who underwent a trial of labor at term with a vertex singleton gestation at an urban tertiary medical center from May 2015 to December 2018 were reviewed. Demographic and clinical data were collected retrospectively. Associations between maternal characteristics and success of vaginal birth after cesarean delivery were assessed using univariate and multivariable logistic regression. Predicted vaginal birth after cesarean delivery success rates using the Maternal-Fetal Medicine Units calculator were compared with actual outcomes (ie, successful trial of labor after cesarean delivery/vaginal birth after cesarean delivery vs repeated cesarean delivery) across each racial and ethnic group.

Results: A total of 910 patients met eligibility criteria and attempted trial of labor after cesarean delivery; 662 (73%) achieved vaginal birth after cesarean delivery. The rate of vaginal birth after cesarean delivery was highest among Asian women (81%) and lowest among Black women (61%). Univariate analyses demonstrated that success of vaginal birth after cesarean delivery was associated with maternal body mass index <30 kg/m², history of vaginal delivery, and absence of indication of arrest of dilation or descent for previous cesarean delivery. Multivariate analyses evaluating predictors of vaginal birth after cesarean delivery reported in the 2021 calculator showed that maternal age, history of arrest disorder for previous cesarean delivery, and treated chronic hypertension were not significant in our patient population. Most patients who were of White, Asian, or "Other" race with a vaginal birth after cesarean delivery had a 2007 calculator-predicted probability of vaginal birth after cesarean delivery of >65%, whereas most Black and Hispanic patients with a vaginal birth after cesarean delivery were more likely to have a predicted probability of vaginal birth after cesarean delivery between 35% and 65% (P<.001). Most White, Asian, and Other-race patients with a repeated cesarean delivery had a 2007 calculator-predicted probability of vaginal birth after cesarean delivery of >65%, whereas most Black and Hispanic patients with a repeated cesarean delivery had a predicted probability of vaginal birth after cesarean delivery between 35% and 65%. Across all racial and ethnic groups, most patients with a vaginal birth after cesarean delivery had a 2021 calculator-predicted probability of vaginal birth after cesarean delivery of >65%.

Conclusion: The inclusion of race/ethnicity in the 2007 Maternal-Fetal Medicine Units vaginal birth after cesarean delivery calculator underestimated predicted vaginal birth after cesarean delivery success rates among Black and Hispanic patients receiving obstetrical care at an urban tertiary medical center. Thus, we support the use of the 2021 vaginal birth after cesarean delivery calculator without race/ethnicity. Excluding race and ethnicity from vaginal birth after cesarean delivery counseling may be one way in which providers can ultimately contribute toward the reduction of racial and ethnic disparity in maternal morbidity in the United States. Further research is needed to understand the implications of treated chronic hypertension for the success of vaginal birth after cesarean delivery.