Does adding a Foley to misoprostol lower risk of cesarean in obese women?

By Judith M. Orvos, ELS

Risk of labor induction and cesarean delivery is increased in nulliparas who are obese, and use of misoprostol or insertion of a Foley balloon often fails in these patients, for reasons that aren’t fully understood. In a new study, investigators examined whether combining the two methods would lower rates of cesarean delivery in this population.

Published in The American Journal of Perinatology, the open-label, comparative-effectiveness, randomized, controlled trial enrolled obese nulliparas with unfavorable cervices at three tertiary centers from January 2016 to June 2018. The participants were randomized 1:1 to either a Foley balloon and misoprostol combined or misoprostol alone. Further management was deferred to treating physicians once the women reached a Bishop’s score > 6. It should be noted that the cesarean delivery background rate for nulliparous obese women being induced at this institution was 53%, meaning that there was a lower threshold for cesarean delivery within the practice. 

The primary outcome of the study was the rate of cesarean delivery. Secondary maternal outcomes included duration of induction-to-delivery interval, occurrence of tachysystole, clinical chorioamnionitis, need for operative vaginal delivery, and a compositive of maternal morbidity. Second neonatal outcomes included need for neonatal intensive care unit admission, transient tachypnea in the newborn, respiratory distress syndrome, meconium aspiration syndrome, culture-proven sepsis, neonatal seizures, and a composite of neonatal morbidity.

A total of 113 women were treated with a Foley balloon and misoprostol and 123 with misoprostol alone. The rate of cesarean delivery was similar between the two groups: 45% vs 43%, P = 0.84; relative risk [RR]: 1.03, 95% CI; 0.75 to 1.42). Occurrence of tachysystole resulting in fetal heart rate abnormalities also did not differ between the two groups: 8.8% vs 16.2%; P = 0.09, RR: 0.54, 95% CI: 0.27 to 1.11).

Total induction-to-delivery interval, too, was similar, regardless of method of delivery: 24.8 ± 13.8 vs 24.5 ± 14.0 hours, P = 0.87). The authors noted, however, a “marginally shorter” average duration of oxytocin infusion after cervical ripening was completed in the women in the combination group (7.4 ± 4.5 vs 8.6 ± 4.8 hours, P = 0.05), which results in a shorter overall duration of the first stage of labor (20 ± 2.6 vs 24.9 ± 5.9 hours, P < 0.01). But second-stage labor was longer in the combination group (1.43 ± 1.1 vs 1.15 ±0.5 hours, P < 0.01).

While acknowledging that low enrollment of eligible women was a major limitation of their study, the authors said that “the relative risk of [cesarean delivery] of 1.03 between the two groups made it unlikely that the addition of more study subjects would have significantly changed our findings.” Well-defined randomized trials in obese nulliparas with unfavorable cervices are needed, they believe, “comparing agents with similar pharmacokinetic and pharmacokinetic profiles, as well as clear definitions of efficacy and safety outcomes.”