Hormonal contraception

The combination hormonal contraceptive pill consisting of a fixed ratio of a progestational compound to an estrogenic compound administered from the 5th to 25th day of the cycle approaches 100% in efficacy. Cycle control is excellent and is related to the mechanism of action. The progestogen plus estrogen of the combination pill inhibit the hypothalamic-anterior pituitary-ovarian axis, thus insuring almost complete inhibition of ovulation and endogenous steroid hormone biosynthesis. The lack of endogeneous hormone is not critical since the pill replaces the lost hormones particularly as to uterine endometrial stimulation so that the tissue is prepared for a bleed on treatment withdrawal. The carefully timed hormonal replacement ensures excellent cyclicity. Although suppression of ovulation may be continued for years, cessation of treatment is followed by a return to normal hormonal function and fertility.Variants of the combination treatment include a once-a-month pill and a once-a-month injectable preparation. Both formulations are based on combinations of a progestogen plus estrogen.A high degree of efficacy approaching that seen for the combination pill has been achieved with a sequential regimen. In this procedure an estrogen alone is administered for 5 to 15 days while a mixture of estrogen plus a progestational agent is administered for the balance of the 20 days of treatment. Withdrawal of treatment brings on a bleed in 2 to 5 days. The mechanism of of antifertility is similar to that of the combination pill.Contraceptive efficiency of a high order may be attained with a small continuous dose of a progestational agent. The pregnancy rate and cyclicity are acceptable but not as good as that of the combination or sequential regimens. The pure progestogen treatment has been adapted to a pseudo post-coital therapy where one sexual contact requires one pill usually within 1 to 3 hours of the event. Thus far a reasonable efficacy has been established but as much as 33% of the cycles may be less than 20 days in length.A Single injection of a progestogen can produce effective antifertility for 90 days. This treatment is efficacious but the early treatment periods may involve considerable irregular bleeding and after repeated use ammenorrhea may be a problem.A true post-coital treatment has not been established. However, for emergency use 4 to 6 days of treatment with high doses of estrogen is highly effective in preventing pregnancy. The mechanism may involve speeding of ova transport thus preventing implantation.