Should we use Foley catheters for preinduction cervical ripening?

BACKGROUND: Pharmacologic methods of cervical ripening are associated with uterine contractile abnormalities. This randomized trial compares intravaginal misoprostol to transcervical Foley catheters for preinduction cervical ripening.

POPULATION STUDIED: A total of 111 pregnant women were admitted to a tertiary hospital for induction. Subjects had singleton vertex pregnancies at more than 28 weeks’ gestation and a Bishop score of less than 6; indications for induction included preeclampsia, oligohydramnios, postdates, and growth restriction. Exclusion criteria included previous uterine surgeries, rupture of membranes, previous induction, or use of a pre-induction agent during the pregnancy. Mean age was 26 years; 70% were nulliparous. Labor was managed actively with rupture of membranes as soon as possible, use of oxytocin, and an epidural rate of almost 90%. Although the study population included premature infants and the setting was different from that in which most family physicians deliver babies, the results probably apply to patients cared for by family physicians.

STUDY DESIGN AND VALIDITY: The participants were randomized with concealed allocation to placement of a transcervical Foley catheter or 50 mg intravaginal misoprostol. A 16F Foley catheter was inserted under direct visualization during a sterile speculum examination without an obturator, tenaculum, or cervical cleansing. Once past the internal os, the balloon was filled with 30 cc of sterile water, and gentle traction was applied (the end of the catheter was taped to the patient’s medial knee or thigh). Every 6 hours the catheter was adjusted to continue traction. In the misoprostol group, 50 μg was placed in the posterior fornix of the vagina every 4 hours up to 6 times. Oxytocin was begun after extrusion of the catheter or 4 hours after the last dose of misoprostol if no labor ensued or if all 6 doses had been given. Bishop scores were assigned before randomization and at the time of Foley catheter extrusion or last dose of misoprostol. The Student t test, Fisher exact test, Mann-Whitney U, and chi square were used to compare groups; no information was given about whether testing was by intention to treat. The methodologic strength of this study was adequate. Its major strengths were randomization with concealed allocation and adequate power. Major weaknesses included the lack of attention to potential confounding factors, such as labor support, that are known to influence the course of labor and the inability to mask the physician assessing the Bishop scores. Other minor weaknesses included the intrinsic lack of intra- and inter-observer reliability of the Bishop score, the possible variation in the timing of giving the Bishop score for the misoprostol group, and the lack of power for assessment of outcomes other than the primary ones.

OUTCOMES MEASURED: The primary outcome measure was change in Bishop score. Secondary outcome measures included length of time for preinduction cervical ripening, total time for induction, delivery route, uterine tachysystole, side effects, subject comfort, and other fetal heart rate disturbances. Cost, patient satisfaction, and neonatal outcomes were not addressed.

RESULTS: The groups were similar at baseline. There was no difference between the groups in change of Bishop score, preinduction cervical ripening times, total induction times, or mode of delivery. However, misoprostol-treated women were statistically more likely to have uterine contractile abnormalities (P <.001; number needed to harm [NNH]=5) and meconium passage (P=.01; NNH=6). Two women in the misoprostol group had hyperstimulation and required cesarean deliveries, but the infants did well. The most frequent complaint in the Foley group was mild discomfort at insertion, but there was no difference between the groups in overall maternal discomfort.