Studies on low-dose oral contraceptives: cervical mucus and plasma hormone changes in relation to circulating D-norgestrel and 17alpha ethynyl-estradiol concentrations.

A study was undertaken to determine the effects of a low-dose oral contraceptive comprising 150 mug of D-norgestrel and 30 mug of 17alpha-ethynyl estradiol (Microgynon) on the plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17BETA-ESTRADIOL, AND PROGESTERONE AND ON THE PHYSICAl properties of cervical mucus. Samples of blood and cervical mucus were obtained from three women during a treated cycle and the immediately-following "withdrawal" cycle. Specific radioimmunoassay methods were used to determine LH, FSH, 17beta-estradiol, and progesterone levels in treated and withdrawal cycles, and D-norgestrel and 17alpha-ethynyl estradiol in samples obtained during treated cycles. The concentration of synthetic steroids was also measured in blood samples obtained before and 1 hour after ingestion of the contraceptive to determine the maximal daily variation. The results indicated that the contraceptive action of this combined low-dose oral contraceptive is mediated through suppression of ovulation and by rendering the cervical mucus impenetrable to sperm. Plasma FSH levels appeared to be one of the most sensitive indices of suppression. Determination of D-norgestrel and 17alpha-ethynyl estradiol showed that 3 to 4 days were required to reach maximal plasma levels and that daily fluctuations were considerable. Withdrawal of the pill resulted in an immediate return to ovulatory cycles in all three subjects studied.