Emergency contraceptive treatment, also known as the "morning-after pill," can remain effective for up to five days after unprotected sexual intercourse. This has just been shown in a study conducted by Dr. Isabel Rodrigues and Dr. Fabienne Grou, both members of the department of family medicine at the Université de Montréal and physicians at the CLSC du Marigot in Laval.

The treatment, prescribed to avoid an unwanted pregnancy when no other means of contraception was used, must ordinarily be administered within 72 hours after intercourse. "Clinical studies of women have always focused on this 72-hour period, but we knew it was theoretically possible that effectiveness might last up to five days after sexual contact," Isabel Rodrigues points out.

The estrogens and progesterone contained in the morning-after pill work either by preventing fertilization of the egg or by preventing a fertilized egg from implanting itself in the wall of the uterus. "If the fertilized egg is already implanted in the uterus, which normally happens on day five, this pill will have no effect and will not cause abortion," Dr. Rodrigues explains. "There is, however, an abortion pill, the RU-486, which may be effective past five days, but it's not yet on the market in North America."

To obtain these results, the two researchers compared real pregnancy rates among women who had taken the emergency contraceptive with the rate of pregnancy risk calculated according to their menstrual cycle. Roughly 300 women, age 14 to 38, took part in the study. They were divided into two groups based on the time elapsed between sexual intercourse and treatment. Among these, 131 women were treated within 72 hours and 169 were given the pill between 72 and 120 hours after intercourse.

Based on menstrual cycles among women in the first group, eight to 10 pregnancies should have been expected. However, only one case of fertilization was observed. The effectiveness rate of emergency contraception in this group was 87% to 90%. In the second group, the number of pregnancies should have been 11 to 14. But only three occurred, indicating an effectiveness of 72% to 79% when treatment was administered up to five days after intercourse. In a sub-group of women with perfectly regular cycles, the rate was as high as 87%.

For the researchers, the message is clear: women who fear an unwanted pregnancy after unprotected sex should see their doctor as soon as possible. But if they can't within the first 72 hours, there's still no reason for them to give up on emergency contraception.

Researcher: Fabienne Grou et Isabel Rodrigues
Phone: (450) 975-5360
Funding: Fédération des médecins omnipraticiens du Québec, CLSC du Marigot