Contraception with a norethisterone-releasing IUD. Plasma levels of norethisterone and its influence on the ovarian function

Abstract

Five healthy women had a norethindrone (NET)-releasing intrauterine device inserted postmenstrually. During a treatment time ranging between 80 and 114 days, plasma concentrations of NET, estradiol, and progesterone were determined by radioimmunoassay. Initial high plasma concentrations of NET were followed by fairly constant levels between 200 pg/ml and 400 pg/ml. Ovulation occurred regularly during nine out of sixteen studied treatment cycles, four cycles were anovulatory and three cycles showed a suppressed luteal phase. High estradiol peaks in plasma were seen at the time of disturbed ovulation. The bleeding pattern was regular and the menstrual bleeding was reduced in amount.