(871) Maternal Fetal Medicine Unit (MFMU) vaginal birth after cesarean calculator validation at academic community hospital

The MFMU vaginal birth after cesarean (VBAC) calculator was revised in 2021 due to concerns that the original 2007 calculator propagated health disparities by including race and ethnicity. The objective of our study was to compare predicted success rates of the 2007 vs 2021 calculators in a population who underwent a trial of labor after cesarean (TOLAC).

Study Design:

This is a retrospective cohort study of pregnant individuals > 18 years who underwent TOLAC after 1 cesarean (CD) at our institution between 9/1/19-8/31/2022. Success scores were calculated using both calculators, categorized (< 50%, 50-59%, 60-69%, and >70% success), and compared, stratifying by race. Receiver operating characteristic (ROC) curves were created to compare the overall performance of both calculators using these predicted success categories.

Results:

2009 individuals with a history of CD delivered during the study period, of which 1291 had one previous CD and no contraindication to TOLAC. Of these, 457 attempted TOLAC, with an overall VBAC success rate of 76.4%. Success rates by race are shown in Table 1. When applying both calculators to this population, a higher proportion of Black individuals had lower predicted success score categories compared to other races when using the 2007 calculator but not the 2021 calculator (Table 2). The overall ability to predict VBAC success was similar for the two calculators (area under the curve for the 2007 calculator 0.70 vs 0.72 for the 2021 calculator, p=0.27).

Conclusion:

In our population, predicted VBAC success rates were lower for Black women when using the 2007 vs 2021 MFMU VBAC calculator, while both calculators performed similarly in predicting overall VBAC success. Our data validate the 2021 revised MFMU VBAC calculator without race or ethnicity.