High-risk pregnancies for maternal, fetal, or placental complications often necessitate induction of labor in the late preterm or early term period for delivery. Limited data exist on the safest method for inducing this specific patient population.
To compare the combination of oxytocin plus Cook balloon versus misoprostol plus Cook balloon for induction of labor in high-risk pregnancies.
We conducted an open-label randomized controlled trial at a single institution from July 2020 to May 2022. The study was approved by Institutional Board Review and registered on ClinicalTrials.gov (NCT04492072). Individuals with high-risk pregnancy, at least ≥ 22 weeks’ gestation, with a singleton in cephalic presentation, Bishop score ≤ 6, and intact membranes were offered enrollment. High-risk pregnancy was defined by the presence of any of the following: hypertensive disease of pregnancy, fetal growth restriction, oligohydramnios, suspected placental abruption requiring delivery, uncontrolled pre-gestational diabetes, or abnormal biophysical profile or non-stress test requiring delivery. The primary outcome was the rate of cesarean delivery. Secondary maternal outcomes included induction to delivery interval, number of vaginal deliveries within 24 hours, rates of uterine tachysystole, intra-amniotic infection, operative vaginal delivery, and postpartum hemorrhage. Secondary fetal outcomes included fetal heart rate abnormalities, stillbirth, Apgar scores less than 7 at 5 minutes, admission to the neonatal intensive care unit (NICU), arterial umbilical blood pH < 7.1, sepsis and neonatal death. A subgroup analysis was planned on the primary outcome to assess the different indications for cesarean delivery. An intent-to-treat analysis was performed.
During the 22 months of the trial, a total of 150 patients were randomized, with 73 (49%) induced with oxytocin and Cook balloon, and 77 (51%) with misoprostol and Cook balloon. There was no significant difference in the overall rate of cesarean delivery between study groups, (21.9% vs 31.1%; RR 0.70, 95% CI 0.41-1.21), nor for those cesarean delivery performed for a specific indication. There were no differences in secondary maternal and fetal/neonatal adverse outcomes.
In high-risk pregnancies, the rate of cesarean delivery and adverse maternal and fetal outcomes were similar for induction of labor with oxytocin and Cook balloon compared with misoprostol and Cook balloon.

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