The phasic approach to oral contraception: the triphasic concept and its clinical application.

The phasic approach to oral contraception is described with a historical review of the evolution of new administration regimens aimed at lowering total steroid content from monophasic to biphasic to the new triphasic approach. The phasic regimen designs which support the intended mechanism of action of each of the phasic approaches are discussed. Emphasis is placed on the discussion of the rationale for the new triphasic oral contraceptive and the clinical demonstration of the triphasic's inhibition of ovulation and maintenance of functional integrity of the pituitary-ovarian axis. A new theoretical formula and practical concept are presented that incorporate a progestogen potency factor, and consequently provide a common denominator enabling a comparison of the magnitude of the effects of various oral contraceptive products on pituitary responsiveness. Widespread clinical studies are described which reinforce the suggestion that the triphasic is the state of the art and represents an important contribution to contraceptive technology.