Emergency Contraception: How Effective Is It?

The most commonly used method of emergency contraception today is the Yuzpe regimen, which was developed some 25 years ago. It basically involves taking an increased dose of an oral contraceptive and it has been called the "morning after pill". An initial dose of two pills comprising 100 µg ethinylestradiol plus 500 µg levonorgestrel, or 1 mg dl-norgestrel, is followed 12 hours later by a dose of two more pills. Traditionally it has been recommended that the first dose of pills is taken within 72 hours of an act of unprotected intercourse.

Until recently, the Yuzpe regimen of combined oral contraceptive pills has been the only hormonal method available for emergency contraception. It prevents about 75% of pregnancies that would otherwise be expected to occur: approximately 8% of women can be expected to become pregnant after a single act of unprotected intercourse on a random day of the menstrual cycle, but only about 2% become pregnant if they use the Yuzpe regimen.

An alternative and more effective method is the insertion of a copper intrauterine device (IUD) by a trained service provider. If inserted within five days of unprotected sexual intercourse, the copper IUD prevents pregnancy in 99% of cases.

Neither of these methods is fully satisfactory for emergency contraception, however. As noted above, the Yuzpe regimen fails to prevent about one-quarter of the pregnancies that would be expected to occur following unprotected sexual intercourse. It can also cause unpleasant side-effects: nausea, vomiting, headaches and dizziness are regularly reported by women who have used the regimen.

Emergency contraceptive pills are intended as just that—i.e. for one-time use in emergencies. Indeed, if a woman uses emergency contraceptive pills frequently, her cumulative risk of pregnancy is higher than if she consistently used oral contraceptives, an IUD or barrier methods.

On the other hand, the copper IUD, while certainly effective as a method of emergency contraception, has a certain number of drawbacks. The IUD is usually not recommended for use by young women who have not yet had children, yet it is precisely this group of women who constitute a large proportion of those requesting emergency contraception. The IUD is also unsuitable as a contraceptive method for women at risk of sexually transmitted diseases unless they use an additional barrier method. The IUD use is generally not recommended for women whose pregnancy status is unclear—such as in women who may be pregnant as a result of an earlier act of unprotected sexual intercourse—as IUD insertion in a woman with established pregnancy can lead to serious complications.

The Yuzpe method of emergency contraception works by interrupting a woman's reproductive cycle. Depending on when in the cycle the pills are taken, they can prevent or delay ovulation, may interfere with fertilization of the egg, or block implantation in the uterus wall. Medical science considers that pregnancy has begun when the implantation of a fertilized egg in the lining of a woman's uterus is complete. The process of implantation starts about five days after fertilization and is completed about one week later, just prior to the time of the expected menses. Emergency contraceptive pills are ineffective after implantation; they cannot cause an abortion if the woman is already pregnant.

The Programme has been in the forefront of research on new methods for emergency contraception for the past 10 years and has been investigating two compounds, levonorgestrel and mifepristone, for this purpose. The next two articles summarize the findings of two recent multicentre research projects on the effectiveness and side-effects of these two compounds.

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