Progesterone antagonists on the horizon

Postcoital contraception: present and future options

PURPOSE

This article reviews information on currently available postcoital contraceptives, and discusses recent advances in postcoital contraception, mostly notably RU 486.

METHODS

Postcoital contraceptives, or "morning after pills," are currently available in the form of high dose estrogens, oral contraceptives, danazol and intrauterine devices. These methods are plagued by high incidences of side effects and less than optimal success rates.

RESULTS

Currently, their primary use in the adolescent age group is for victims of sexual assault, but they may also be used as back-up for consensual unprotected intercourse. RU 486, best known as a first trimester abortifacient, has a number of potential uses, including that of a postcoital contraceptive. Two recently published studies from the UK showed RU 486 to have a very low pregnancy rate and fewer side effects when compared with current methods. RU 486 may someday replace high doses of oral contraceptives as the method of choice for postcoital contraception.

Predictors of failed attempted abortion with the antiprogestin mifepristone (RU 486)

The experience of 271 patients who received mifepristone (RU 486) in experimental protocols from July 1984 to January 1989 was analyzed by logistic regression methods. The regimen used was the strongest predictor of failure, followed by Quetelet's index and initial beta-human chorionic gonadotropin level. The relative risk of failure was 2.3 times with 7-day regimens and 6.3 times with the other regimens that obtained with regimens of 600 mg given once or twice. The relative risk of failure increased with increasing Quetelet's index; women in the top quartile were 2.9 times more likely to fail to abort than were women in the bottom quartile. The risk of failure increased with increasing initial beta-human chorionic gonadotropin level; those with an initial level greater than 19,800 mIU/ml were 2.8 times more likely to fail to abort than were women with an initial value less than or equal to 6350 mIU/ml. Body mass appears to influence the likelihood of abortion with mifepristone.