Combined Estrogen–progestogen Contraceptives

Combined hormonal contraceptives consist of an estrogen and a progestogen, and act primarily by preventing ovulation through the inhibition of follicle-stimulating hormone and luteinizing hormone. The progestogen component also renders the cervical mucus relatively impenetrable to sperm and reduces the receptivity of the endometrium to implantation. These mechanisms render combined hormonal contraceptives very effective in the prevention of pregnancy. Annual failure rates vary between 0.02% (two per 10 000 women/year) when full adherence to instructions for use is assumed (Ketting, 1988) and 5% for typical use (Fu et al., 1999). A variety of innovations have been developed since combined hormonal contraceptives were first made available in the late 1950s, but not all of these have proved valuable in practice. Changes in drug components, doses used and the temporal sequencing of exposure to drugs have incorporated new technologies and responded to suggested risks. While regional variations in use are abundant, the dominant trends have been towards less androgenic progestogens, lower doses of estrogen and progestogen, the near abandonment of hormonal contraceptives with an estrogen-only phase, a proliferation of different product formulations and the continuing development of novel delivery systems. In combined hormonal contraception, ethinylestradiol is the most common estrogen, although other are used occasionally. A variety of progestogens is available and these differ in their properties with regard to progestogenic and androgenic characteristics. The estrogen and progestogen contained in combined hormonal contraceptives are usually given in a monthly cycle, and a variety of regimens ensure that the doses of the two constituents