Amniotomy versus Deferral at  cm during Standardized Induction of Labor: A Propensity Score-Matched Study

The present study aimed to determine the specific impact of artificial rupture of membranes (AROM) at first examination ≥ 4 cm versus deferring AROM at that examination while undergoing otherwise standardized labor induction. This is a secondary analysis of a prospective cohort evaluating the implementation of standardized induction of labor (IOL) management of patients undergoing ≥37 weeks of induction at two sites from 2018 to 2022 with a singleton pregnancy, intact membranes, and an unfavorable cervix without prior cesarean delivery (CD). Patients were grouped by whether AROM was performed at the first examination ≥4 cm, or deferred. A 1:1 propensity score matching balanced parameters associated with AROM at the ≥4 cm examination. The primary outcome was time to delivery. Secondary outcomes included length of each stage, CD, and maternal/neonatal morbidity. Time-to-event regression analyses for labor length, censored for CD, were modeled with a Cox proportional hazard model. Among 8,509 inductions in the parent study, 5,784 (67.0%) remained unruptured by the first examination ≥4 cm. After propensity score matching, 1,412 were included (n = 706/group). Overall, AROM was associated with shorter time to delivery compared with deferral at first examination ≥4 cm (21.4 [14.6–29.3] vs. 22.6 hours [16.4–31.3]), p = 0.002), a finding consistent across parity. Once censored for CD, these findings remained significant (hazard ratio [HR] = 1.17, 95% confidence interval [CI]: [1.04–1.31]). There were no differences in CD or morbidity. Even when matching for the induction course prior to the first examination at ≥4 cm, AROM at ≥4 cm is associated with shortened time to delivery without increasing maternal or neonatal morbidity.