Outpatient cervical ripening by nitric oxide donors for prolonged pregnancy: a randomized controlled trial.

OBJECTIVE: To assess whether outpatient cervical ripening at 41 0/7 weeks of gestation with the nitric oxide donor isosorbide mononitrate reduces cesarean delivery rates in nulliparous women with an unfavorable cervix.

METHODS: We recruited nulliparous pregnant women with a Bishop score less than 6 in a randomized, multicenter, double-blind, placebo-controlled trial. Women received 40 mg vaginal isosorbide mononitrate or a placebo at 41 0/7, 41 2/7, and 41 4/7 weeks of gestation. They returned home between visits. At 41 5/7 weeks of gestation, for women who had not yet given birth, labor was induced with oxytocin or prostaglandins, depending on cervical status. We needed 685 women per group to detect a 25% reduction in the cesarean delivery rate, the primary outcome measure, from 25% in the placebo group to 18.75% in the isosorbide mononitrate group (1-β=0.8, α=0.05, two-sided).

RESULTS: The NOCETER (NO donors for reduction of CEsareans at TERm) trial was a negative study. The cesarean delivery rate was 27.3% (185/678) in the isosorbide mononitrate group and 27.2% (186/684) in the placebo group (relative risk 1.00, 95% confidence interval [CI] 0.84-1.19). None of the maternal secondary efficacy outcomes differed between groups. Side effects were more common among women receiving isosorbide mononitrate than in the placebo group (78.8% [534/678] compared with 27.9% [191/684], relative risk 2.82, 95% CI 2.49-3.20). Composite perinatal morbidity did not differ between groups.

CONCLUSION: Outpatient cervical ripening with vaginal isosorbide mononitrate for prolonged pregnancy in nulliparous women does not reduce cesarean delivery rate.

CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00930618.