6: The efficacy of early amniotomy in nulliparous labor induction: a randomized controlled trial


      To assess whether early amniotomy (AROM at ≤ 4cm dilated) reduces the duration of labor or increases the proportion of subjects delivered within 24 hours in term nulliparous patients undergoing labor induction.

      Study Design

      We performed a randomized clinical trial to test our hypothesis. Nulliparous patients with singleton, viable pregnancies undergoing labor induction at or beyond 37 weeks were eligible for inclusion. We excluded subjects with PROM, cervical dilation > 4cm at admission, or significant vaginal bleeding. Eligible subjects were randomized to early amniotomy (AROM at ≤ 4cm) or standard management (AROM at > 4cm). Outcomes for this study included duration of labor, % delivered within 24 hours, cesarean rate, maternal infectious complications, and measures of neonatal outcome. A priori sample size was based on the proportion of subjects delivered within 24 hours of randomization. Assuming alpha error of 0.05, 80% power, incidence of delivery within 24 hours of 50% in the standard management group, and a minimum detectable relative risk of 0.75, we estimated that we would need 290 subjects per group. Analysis was performed using bivariate statistics, under the intent to treat principle.


      We randomized 585 subjects into this clinical trial, 292 into early amniotomy group and 293 into the standard management group. Baseline demographics at randomization, cervical dilation at admission, and methods of induction were similar between the groups. Early amniotomy shortened the time from randomization to delivery by over 2 hours (p=0.04) and increased the proportion of subjects delivered within 24 hours of randomization (Table). There was no effect of early amniotomy on maternal or neonatal infectious complications, or on other measures of neonatal outcome.
      Tabled 1
      OutcomeEarly AmniotomyStandard ManagementRR95% CIp
      Randomization-delivery (hrs)19.021.3--0.04
      % delivered < 24hours from randomization68%56%1.221.07-1.380.002
      Postpartum fever10.4%9.4%1.100.67-1.790.70


      In nulliparous labor inductions, early amniotomy shortens the time to delivery by over 20 percent, and increases the likelihood of delivery within 24 hours, without adversely impacting maternal or neonatal well-being.