(189) Amniotomy Versus Deferral at ≥4cm during Standardized Induction of Labor: A Propensity Score-Matched Study

Objective: To determine the impact of artificial rupture of membranes (AROM) at first exam ≥4cm vs. deferring AROM at that exam while undergoing otherwise standardized labor induction (IOL).

Study Design: This is a secondary analysis of a prospective cohort evaluating the implementation of standardized IOL management of patients undergoing ≥37 weeks IOL at 2 sites from 2018-2022 with a singleton pregnancy, intact membranes, and unfavorable cervix without prior cesarean delivery (CD). For this analysis, patients who underwent AROM or spontaneous rupture at < 4cm were excluded. Patients were grouped by whether AROM was performed at first exam ≥4cm or deferred. 1:1 propensity score matching balanced parameters associated with AROM at the ≥4cm exam, including clinician type (midwife vs. physician), study year, maternal age, parity, gestational age, cervical ripening agent used, and adherence to the IOL protocol prior to the ≥4cm exam, including time from first to last misoprostol if used, and time Foley balloon in place if used. The primary outcome was length of IOL. Secondary outcomes included length of each stage of labor, CD, and maternal/neonatal morbidity. Time-to-event regression analyses for labor length, censored for CD, were modeled with a Cox proportional hazard model. Analyses were stratified by parity.

Results: Among 8509 inductions in the parent study, 5784 (67.0%) remained unruptured by first exam ≥4cm. After propensity score matching, 1592 were included (n=796/group). Overall, AROM was associated with shorter IOL compared to deferral at first exam ≥4cm (21.3h[14.4-29.0] vs. 22.7h[16.1-31.2]), p=0.001; Table), a finding consistent across parity. AROM at first exam ≥4cm was also associated with shorter latent and active phases. Once censored for CD, these findings were no longer significant (Figure). There were no differences by AROM vs. deferral in CD or morbidity.

Conclusion: Even in the context of otherwise standardized IOL management, AROM at first exam ≥4cm may still be associated with shortened IOL without increasing morbidity, but this finding is not significant once censored for CD.