Risk of Uterine Rupture and Dehiscence Among Women Attempting a Vaginal Birth After a Low Vertical Uterine Incision [A232]

INTRODUCTION: The risk of uterine rupture after a prior low vertical (LVCS) is unknown. The objective of this study was to estimate the risk of uterine rupture in individuals attempting a trial of labor after cesarean delivery (TOLAC) with a prior LVCS. METHODS: This is a secondary analysis of the Maternal Fetal Medicine Units Network’s C-section Registry, a multicenter, prospective observational study. We included individuals with term singleton pregnancies undergoing TOLAC with a prior low transverse incision (LTCS) or LVCS and excluded those who received prostaglandins or had a history of myomectomy. Multivariate regression models were used to estimate the relative risk between uterine rupture with a prior LVCS compared to LTCS. After controlling for known confounders, our secondary outcome was uterine dehiscence. RESULTS: In this cohort, 14,773 individuals attempted TOLAC (14,665 prior LTCS; 108 prior LVCS). Uterine rupture occurred in 94 (0.7%) of women with prior LTCS and 1 (0.1%) woman with prior LVCS. Uterine dehiscence occurred in 101 (0.7%) of individuals with prior LTCS and 3 (2.9%) of individuals with prior LVCS. Compared to those with a prior LTCS, the risk of uterine rupture was not different (RR, 1.49; 95% CI, 0.21–10.58). However, the risk of uterine dehiscence was increased among those with prior LVCS (RR, 4.07; 95% CI, 1.31–12.63) compared to prior LTCS. CONCLUSION: Individuals with a prior LVCS have an increased risk of uterine dehiscence, but not uterine rupture, compared to prior LTCS. These results may inform counseling for those individuals considering TOLAC after prior LVCS.