Early luteal phase treatment with mifepristone (RU 486) for fertility regulation

Mifepristone (RU 486) is an antiprogestin which interacts with progesterone at the receptor level. Administration of mifepristone immediately after ovulation does not upset the menstrual cycle. However, the maturation and function of the endometrium is inhibited and uterine contractility is changed. To test if these effects are sufficient to prevent implantation, 21 women agreed to use one single treatment with 200 mg mifepristone on day luteinizing hormone (LH) + 2 monthly as their only contraceptive method. The women were treated for 1– 12 months. The time of the LH peak was determined in the urine by the women themselves using a rapid LH test (Ovu-quick, Organon). The overall number of cycles studied was 169. In 12 cycles the women were unable to detect the LH peak. In these cycles no treatment was given and the women advised to use barrier methods during the time to menstruation. The remaining 157 cycles with a detectable LH peak were all ovulatory based on plasma progesterone measurement. One pregnancy occurred. On the basis of the time of the LH peak, it was retrospectively calculated that in 124 cycles at least one act of intercourse occurred during the period 3 days before to 1 day after ovulation. The probability of pregnancy in this period of the menstrual cycle is thus 0.008. The women did not complain of any treatment-related side-effects apart from slight bleeding for 2–3 days starting a few days after the day of treatment in 35% of the cycles. The results show that the effect of mifepristone on the endometrium is sufficent to prevent pregnancy and indicate that treatment with antiprogestin can also be used for contraceptive purposes.