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Preventing pregnancies to prevent abortions.

Short of abstinence, the oral use of a combination of an estrogen and a progestin has been the most effective method of contraception yet devised, with a 99-100 percent success rate. Starting five days after the onset of a menstrual period, the combination pill is taken daily for 20 or 21 days. The next course is then taken seven days after the last dose, or five days after menstrual flow begins, whichever comes first. (Alternatively, one may simply take a daily pill for three weeks, stop for one week, and then resume the three-week cycle, regardless of when menstruation starts or stops.)

Other modifications of steroidal contraception also have been used with success. Sequential preparations, in which an estrogen was taken for 14 to 16 days and a combination of an estrogen and a progestin then taken for five or six days, have been about 98-99 percent effective. These, however, have been removed from the market because of reports suggesting an increased incidence of endometrial tumors and a lower efficacy.

Preparations containing only a single hormone (estrogen or progestin) also have been available. Those containing only a progestin are called "minipills." The minipill was introduced because the estrogen in combined preparations was thought to be responsible for most of the side effects of oral contraceptives. It has been less popular, however, because it is only 97-98 percent effective, and menstrual cycles are more irregular.

The After-Intercourse Pill: Standard Treatment vs. Mifepristone

In the study reported from England in our January issue, emergency (postcoital) contraception consisted of a large dose of an estrogen given within 72 hours after intercourse with a small dose of a progestin, each given twice, 12 hours apart, for five days. This therapy was compared with the use of the synthetic hormone mifepristone, given in a single dose of 600 mg.

The function of the estrogen component is to inhibit ovulation, while progestin ensures that menstrual bleeding occurs promptly upon withdrawal of the estrogen, that it will be brief, and that it is essentially normal in other respects.

A fertilized ovum requires about seven days to travel down the Fallopian tube and become implanted in the endometrial lining of the uterus. For implantation to occur, the endometrium must be in just the right stage of its monthly development under the influence of the woman's own estrogen and progesterone secretions.

The large doses of estrogen used for postcoital contraception (the morning-after pill) probably act upon the entire genital tract from the ovary to the uterus. The estrogen may change the normal motility of the Fallopian tube enough to hinder the passage of the fertilized ovum. It also may change the endometrium, causing it to bleed when the estrogen is withdrawn. Whatever its method of action, it effectively prevents the fertilized ovum from becoming implanted--and pregnancy does not take place.


The French drug RU 486 (mifepristone) is a synthetic steroid that blocks the action of progesterone on the endometrium. When given before the fertilized ovum has reached the uterus, it prevents implantation. When given before the sperm reaches the ovum, it can prevent fertilization.

Using RU 486 as a postcoital contraceptive has its benefits. Given within 72 hours of unprotected intercourse or a contraceptive failure (such as a tom condom), the drug effectively prevents pregnancy, with significantly fewer side effects than the standard therapy.

Some may argue, incorrectly, that pregnancy begins at fertilization, and if RU 486 acts by preventing implantation of the fertilized ovum, the result is an abortion. Implantation does not begin until five or six days after fertilization, and is complete eight days later. Pregnancy does not begin, therefore, until implantation is complete, for only then is the fertilized ovum able to develop into a fetus. (In so-called "test tube" pregnancies, in which the ovum is fertilized outside the woman's bedy, there is certainly no pregnancy until the ovum is successfully implanted in her uterus.)

In the October 8, 1992, New England Journal of Medicine, where the British report on RU 486 appeared, an editorial notes that many women--and health care professionals-are unaware of the availability of postcoital (emergency) contraception. Such ignorance is unacceptable, if we are to deal successfully with the enormous problem of undesirable pregnancies in this country. Even for those individuals who seek "morning-after" contraception, the side effects of the therapy currently being employed may deter them from completing the full course of treatment.

The demonstrated effectiveness of RU 486 as a postcoital contraceptive could have a significant impact on the prevention of undesirable pregnancies-and an unwanted pregnancy prevented is a potential abortion avoided.
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Publication:Medical Update
Date:Mar 1, 1993
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