MFMU TOLAC Calculator: Does knowledge of a predicted success score increase VBAC rates?

Objective: The Maternal Fetal Medicine Units (MFMU) Network developed a calculator to determine a Trial of Labor after Cesarean (TOLAC) success score based on maternal age, BMI and OB history. Despite wide-spread adoption, it is unclear whether provider knowledge of a predicted score alters the likelihood of a successful vaginal birth after cesarean (VBAC). We aimed to determine whether provider knowledge of the MFMU calculated TOLAC score effects VBAC rates. Study Design: A retrospective cohort study of all patients undergoing a TOLAC from a single academic medical center between 2018-2020 was conducted. During this period, the MFMU TOLAC calculator (calculator version 1, released 2017) was gradually being incorporated into clinical care, allowing for a direct comparison between patients in which the predicted success score was known to providers vs. those in which a score was not calculated. Data, including the number of prior vaginal/cesarean births, race/ethnicity, BMI, as well as other predictors were collected and analyzed. The actual VBAC rates for both groups were compared. Results: 204 consecutive TOLAC deliveries were included in the analysis, 153 of which (75%) had a successful VBAC. The MFMU TOLAC score was calculated at the time of admission in 79 (39%) cases. Overall, the calculator was accurate in those with a 50-60% and 80-90% likelihood of success, and underestimated the actual VBAC success rate in those with a 60-70% and 70-80% likelihood of success (figure 1). The group in which a score was calculated had a higher BMI at delivery and had a lower incidence of a previous VBAC. (Table 1). VBAC success rates were similar between the groups (78.5% in those with vs. 70.89% in those without a TOLAC score, p = 0.316). Conclusion: Provider knowledge of the MFMU calculated TOLAC success score did not appear to impact actual VBAC rates. The ways in which high- and low- TOLAC scores affect actual VBAC rates and outcomes warrant further investigation. [Formula presented] [Formula presented]