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.(ABSTRACT TRUNCATED AT 250 WORDS)
PIP: Mifepristone (RU-486) is an antiprogestin which interacts with progesterone at the receptor level. The objective was to determine whether the effects on endometrial development and function and on uterine contractility of immediate post-ovulatory treatment with mifepristone could prevent pregnancy. 21 fertile, sexually active women with regular menstrual cycles were treated with a single dose of 200 mg mifepristone 2 days after the luteinizing hormone (LH) surge (LH + 2) on a monthly basis 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), and this was confirmed later by radioimmunoassay. All the women, except one, had previously had at least 1 delivery and 1 pregnancy terminated. Each woman measured the urine concentration of LH twice daily, starting about 4 days prior to the expected time of ovulation (normally day 10 of the cycle) and continuing until 1 day after the maximum LH concentration. The plasma concentration of progesterone was measured 5 days and human chorionic gonadotrophin (HCG) 2 weeks after the treatment in all cycles. The overall number of cycles studied was 169. In 12 cycles the women were unable to detect the LH peak. The remaining 157 cycles with a detectable LH peak were all ovulatory based on plasma progesterone measurement. 1 pregnancy occurred and was terminated by vacuum aspiration. Based on the time of the LH peak, it was retrospectively calculated that in 124 cycles at least 1 act of intercourse occurred between 3 days before and 1 day after ovulation. The probability of pregnancy in this period of the menstrual cycle was thus 0.008. The were no 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 effect of mifepristone on the endometrium was sufficient to prevent pregnancy, therefore it can be used for contraception.