Labor induction in women at term with mifepristone (RU 486): a double-blind, randomized, placebo-controlled study

To determine the efficacy and safety of mifepristone as an induction agent for the initiation of labor or as a cervical ripening agent in women at term.

Our study group contained 120 women at term (after 37.5 weeks' amenorrhea) who had clear clinical indications for labor induction. They were randomized to receive either 200 mg of mifepristone or placebo on days 1 and 2 of a 4-day observation period, with labor induction planned for day 4. Eight patients, three treated with mifepristone and five receiving placebo, had to be excluded from the survey because they required cesareans for medical reasons (fetal distress or maternal complications) less than 12 hours after taking the first tablet.

Forty-one subjects entered spontaneous labor, 31 treated with mifepristone and ten in the control group (P < .001). Forty-five needed cervical maturation with prostaglandins on day 4, 13 of whom had received mifepristone and 32 of whom had been given placebo (P < .001). Thirteen women treated with mifepristone and 13 who had taken placebo had mature cervices sufficient for classic labor induction with oxytocin and amniotomy. Patients who delivered vaginally needed a much lower amount of oxytocin when mifepristone had been given, and the mean time interval between day 1 of the survey and the onset of labor was also significantly shorter in this group.

Although more studies are needed, we have found mifepristone to be a safe, efficient, and suitable induction agent for initiation of labor in women at term.