Cervical Ripening for Obese Women: A Randomized, Comparative Effectiveness Trial

Obese pregnant women (BMI ≥ 30 kg/m2) are more likely than their normal-weight counterparts to require induction of labor because of increased rates of obstetric complications including pregnancy related hypertensive disorders, diabetes, and prolonged gestations. Several studies have shown that obese women experience increased labor duration and oxytocin needs when compared to normal-weight women. This in turn results in increased rates for unplanned cesarean delivery (CD) as a result of failed induction of labor (IOL), arrest disorders and non-reassuring fetal heart rate tracing, that is dose-dependent with increasing class of obesity. The investigators hypothesize that obese pregnant women and unfavorable cervix (Bishop score ≤ 6), IOL ≥ 24 weeks gestation using the Foley balloon plus vaginal misoprostol will result in reduced cesarean delivery rates when compared to vaginal misoprostol alone.

Nulliparous pregnant women at ≥ 32 weeks' gestation admitted to labor and delivery for IOL and who meet the inclusion and exclusion criteria will be approached by the research staff. Group 1 will be composed of women allocated to the Foley balloon plus misoprostol. These women will receive vaginal misoprostol per standard protocol at 25 micrograms every 4 hours. In addition, a 26 Fr-Foley balloon catheter will be inserted by routine clinical standards. The Foley will be inserted through the internal cervical os, filled with 60 mL of normal saline, and then pulled snugly against the internal os. The catheter of the Foley will be taped to the patient's inner thigh under gentle traction. If the Foley is unable to be placed, the patient will be reexamined in 1 hour and placement will be reattempted if Bishop's score is still 6 or less by the healthcare provider. When the Foley balloon had fallen out or had to be removed because 12 hours have passed since insertion as per protocol, further management of labor will be left at the discretion of the labor team.

Group 2 will be composed of women allocated to vaginal misoprostol-only. These women will receive 25 micrograms of misoprostol per vagina every 4 hours. Once the cervix becomes favorable (Bishop score \> 6), misoprostol administration will be discontinued. Similarly, further management will be left at the discretion of the labor team.

In both groups, if IV oxytocin is indicated, it will be withheld until 4 hours after the last dose of misoprostol to prevent uterine hyperstimulation. Other aspects of labor management will be similar for both groups, including continuous electronic fetal monitoring with external Doppler device or fetal scalp electrode. Uterine contraction assessment will be performed with either an external tocodynamometer or an intrauterine pressure catheter.

Eligibility Criteria:
Inclusion Criteria

* Nulliparous women aged 18 or above
* BMI ≥ 30 at the time of labor induction
* Singleton gestation
* Cephalic presentation (includes successful external cephalic version)
* Intact fetal membranes
* Unfavorable cervix (Bishop score of ≤ 6)
* Gestational age ≥ 32 weeks

Exclusion Criteria

* Patient not candidate for IOL with misoprostol as deemed by the treating physician
* Multiple gestation
* Major fetal anomalies
* Fetal demise