Residual ovarian activity during oral steroid contraception

Steroid drugs with contraceptive properties have been available in the clinical setting for over four decades and are still subject to improvement. Estrogens, progestins and anti-progestins have been used alone or in various combinations, regimens and routes of administration to favour the balance between efficacy and undesirable effects. One of the most important changes in this respect is the gradual lowering of steroid dosage in commercially available contraceptives. Current steroid contraceptive pills still achieve the goal of suppression of pituitary-ovarian activity, but the margins for error are minimal. In this review the available data on modes of action and the effects on suppressing pituitary-ovarian activity by different forms of oral contraception are reassessed. Although pregnancy rates provide a crude measure of contraceptive efficacy, no benchmark for pituitary-ovarian inhibition is available to test the suppressive potential of contraceptive drugs. Consequently, many studies provide incomplete and/or incomparable results. For the further study of those forms of steroid contraception that rely predominantly on suppression of ovarian activity, prevention of dominant follicles selection should be the objective.