Postovulatory contraception in women with large doses of norethindrone

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The postovulatory administration of large doses of norethindrone to women has previously been shown to drastically reduce the peripheral plasma levels of progesterone. In 10 treatment cycles, compared to 10 control cycles from the same women, this effect was confirmed and a similar effect upon the peripheral plasma levels of estradiol was found. The contraceptive efficacy of this treatment was tested. Eighty volunteers were treated during 301 cycles. Eighty per cent of the women had been pregnant before. The plasma levels of progesterone and estradiol were determined before and after treatment in each cycle. A very sensitive test for the detection in serum of human chorionic gonadotrophin (HCG) was included. A total dose of 200 mg of norethindrone was used in two different schedules (100 mg daily on day 21–22 and 50 mg daily on day 19–22). Twenty-two pregnancies occurred, but in 4 of these women, the only indication of pregnancy was the detection of HCG. Two women did not take the tablets according to schedule, leaving 16 patients who had to be aborted therapeutically. At least 70 per cent of the cycles were found to be ovulatory. Control of vaginal bleeding was good and only minor side effects occurred. The treatment possibly reduced fertility in this group of women but the contraceptive efficacy was obviously too low to merit further use of the present dose and schedules.