VBAC calculator 2.0: Recent evidence

Following criticism for the use of race as a biological predictor of vaginal birth after cesarean (VBAC), an updated version of the Society for Maternal-Fetal Medicine (SMFM) VBAC calculator has been published. The variable "African American" or "Hispanic" (yes/no), which produced systematically lower chances of VBAC for nonwhites has been replaced with "chronic hypertension requiring treatment" (yes/no). Although there are no published external validation studies to date, developers report accuracy (area under the curve and calibration) nearly identical to the original calculator and it is published online for immediate use. This review examines the history of the calculator, measures of its validity, and recent studies measuring its performance among Hispanics, Blacks, Asians, and others with lower range scores. Underprediction of successful VBAC is evident in the original calculator, especially as predicted VBAC decreases. These studies raise a concern about the use of calculator scores in clinical management, that is, discouraging or restricting access to labor after cesarean (LAC) for parents with lower calculator scores. This raises special concern for minority populations who experience increased cesarean-related morbidity, face obstacles accessing LAC care, and who may benefit disproportionately from increased LAC uptake. Although calculator developers have discouraged using calculator scores to restrict access to LAC, such uses are documented. It is not clear what effect the removal of race will have on calculator performance, and further study is required before calculator scores are used in counseling. This includes studies that include large numbers of low scoring and minority patients.