Comparison of 25 μg Sublingual and 50 μg Intravaginal Misoprostol for Cervical Ripening and Labor: A Randomized Controlled Equivalence Trial

Sublingual misoprostol, used for labor induction, produces earlier and higher peak plasma concentrations of misoprostol than vaginal or rectal misoprostol. The sublingual route could be expected to be more effective and safer than the vaginal route and by avoiding a direct effect on the cervix, it might reduce the risk of uterine hyperstimulation and be safer. This study aimed to compare the efficacy of 25-µg sublingual misoprostol with 50-µg intravaginal misoprostol for cervical ripening prior to labor induction in primiparous women. In a double-blind, parallel randomized controlled equivalence trial, we recruited 131 primiparous women at 36–42 weeks of gestation requiring labor induction who referred to Alzahara hospital in Rasht, Iran. The women were randomly assigned to receive 25-µg sublingual misoprostol with vaginal placebo (n = 63) or 50-µg intravaginal misoprostol with sublingual placebo (n = 63). The dose was repeated every 4 h (maximum 4 doses). The primary outcome was the interval from the start of induction to vaginal delivery. There were no significant differences between the two groups with regard to the interval from the start of induction to vaginal delivery(13.2 ± 3.07 h in the vaginal group vs. 13.1 ± 3.46 h in the sublingual group), duration of active phase, Bishop Scores after 4h, and rate of the vaginal delivery under 12 h. Also, the rate of hyperstimulation, tachysystole, type of delivery, cause of cesarean section, Apgar scores less than 7 and admission to the NICU were similar in these two groups. The mean dose of misoprostol applied was significantly lower in the sublingual group (P = 0.001). Sublingual administration of 25-µg of misoprostol appears to be as effective as 50 µg intravaginal misoprostol for cervical ripening and labor induction.