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LB01: A randomized trial of elective induction of labor at 39 weeks compared with expectant management of low-risk nulliparous women

      Objective

      To test the hypothesis that elective induction of labor (IOL) at 39 weeks compared with expectant management (EM) among low-risk nulliparous women reduces the risk of a composite of perinatal mortality and severe neonatal morbidity.

      Study Design

      In this open-label multi-center RCT, low-risk nulliparous women with reliably determined gestational age were randomly assigned between 38 0/7 weeks and 38 6/7 weeks either to IOL at 39 0/7 - 39 4/7 weeks or EM. A cervical examination to determine modified Bishop score was performed from 72 hours before to 24 hours after randomization. Those in the EM group were expected to forego elective delivery before 40 5/7 weeks and to be delivered no later than 42 2/7 weeks. The primary outcome was a composite of adverse perinatal events (Table). The major secondary outcome was cesarean delivery (CD). A sample size of 6000 women was needed to detect at least a 40% difference in the primary perinatal outcome, assuming 85% power, with a 3.5% frequency of that outcome in the EM group and a 92.5% adherence to the assigned protocol.

      Results

      From March 2014 - August 2017, 6106 women were randomized at 41 hospitals: 3062 to the IOL group and 3044 to the EM group. 94% and 95%, respectively, adhered to the protocol of the assigned group. 63.5% of participants had an unfavorable modified Bishop score (< 5) at the time of randomization. Women in the IOL group delivered significantly earlier than those in the EM group (39.3 weeks (IQR 39.1 - 39.6) vs. 40.0 weeks (IQR 39.3 - 40.7), p<.001). The primary perinatal outcome occurred in 4.4% of the IOL group and 5.4% of the EM group (RR 0.81, 95% CI 0.64 - 1.01; p = .06). Need for neonatal respiratory support was significantly less frequent in the IOL group (Table). The frequency of CD was significantly lower in the IOL group (18.6% vs. 22.2%, RR 0.84, 95% CI 0.76 - 0.93), as was preeclampsia/gestational hypertension (Table). A priori baseline subgroup analyses showed no differences by race/ethnicity, maternal age > 34 years, BMI > 30 kg/m2, or modified Bishop score < 5 (all P-values for interaction > .05) for either the primary perinatal outcome or CD.

      Conclusion

      IOL at 39 weeks in low-risk nulliparous women results in a lower frequency of CD without a statistically significant change in the frequency of a composite of adverse perinatal outcomes.
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