EARLY LUTEAL-PHASE TREATMENT WITH MIFEPRISTONE (RU-486) FOR FERTILITYREGULATION

Mifepristone (RU 486) is an antiprogestin which interacts with progest erone at the receptor level. Administration of mifepristone immediatel y after ovulation does not upset the menstrual cycle. However, the mat uration and function of the endometrium is inhibited and uterine contr actility is changed. To test if these effects are sufficient to preven t implantation, 21 women agreed to use one single treatment with 200 m g mifepristone on day luteinizing hormone (LH) + 2 monthly as their on ly contraceptive method. The women were treated for 1 - 12 months. The time of the LH peak was determined in the urine by the women themselv es using a rapid LH test (Ovu-quick, Organon). The overall number of c ycles studied was 169. In 12 cycles the women were unable to detect th e LH peak. In these cycles no treatment was given and the women advise d to use barrier methods during the time to menstruation. The remainin g 157 cycles with a detectable LH peak were all ovulatory based on pla sma 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 d ays before to 1 day after ovulation. The probability of pregnancy in t his period of the menstrual cycle is thus 0.008. The women did not com plain 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 treat ment with antiprogestin can also be used for contraceptive purposes.