Effects of low-dose mifepristone administration in two different 14-day regimens on the menstrual cycle and endometrial development: a randomized controlled trial.

BACKGROUND: This study was conducted to evaluate the effects of treatment with mifepristone 5 mg given every day or every other day for 14 days, starting 15 days after menses started for endometrial development. STUDY DESIGN: Ten women recruited to the study were given mifepristone 5 mg beginning 15 days after initiation of menses. In Group A, five women were administered mifepristone every day for three cycles; in Group B, five women were administered mifepristone every other day for three cycles. The effects on the menstrual cycle and endometrial development were investigated. RESULTS: Following these treatments with mifepristone 5 mg, there was slight suppression of ovulation in both treatment cycles compared with control cycles. The follicular phase in subsequent cycles was prolonged after daily treatment with mifepristone, which was not observed after administration every other day. In addition, continuous treatment increased progesterone receptor (PR) expression and reduced leukemia inhibitory factor (LIF) expression in the endometrial epithelium. CONCLUSION: Treatment with low-dose mifepristone every day or every other day starting 15 days after initiation of menses retards endometrial development and impairs endometrial receptivity but has minor effects on the menstrual cycle.