Emergency Contraception

The equivalent of four Lo-Ovral birth control pills are taken, followed 12 hours later by four more pills. No additional pills are taken. Other pills that can easily be substituted include Lo-Ovral, Nordette, Levlen, Trilevlen or Triphasil. The medium dose Ovral can also be used, but in this case, only two pills are taken and two more 12 hours later.

Commonly, emergency contraception pills are packaged as a unit dose. In this case, the instructions on the packaging should be followed.

If none of these pills are available, it is likely that any standard low-dose BCP (four pills initially, followed by four more, 12 hours later) will have similar effects. These other preparations have not been studied in as much depth, however, so it is certainly preferable to use one of the listed BCPs.

With the use of emergency contraception, the risk of a pregnancy occurring is reduced by about 75%. Said another way, if 100 women have a single episode of unprotected intercourse during the middle two weeks of their menstrual cycle, normally about 8 of them will conceive. So the general risk of pregnancy following a single unprotected intercourse during the middle two weeks of the menstrual cycle is approximately 8%. If multiple episodes of unprotected intercourse occur, then the likelihood of pregnancy will of course be higher.

If emergency contraception is used within 3 days of this single unprotected intercourse, the likelihood of a pregnancy occurring is reduced from 8% to 2%. This represents a 75% reduction in risk of pregnancy. So emergency contraception will not reduce the risk of pregnancy to zero, but a 75% reduction in risk is still pretty good and is often a good idea.

The greatest experience with emergency contraception has been within the 72-hour window. Some studies find emergency contraception is most effective the sooner it is initiated within that 72 hours. Other studies find no difference in pregnancy rates. A few studies have looked at the use of emergency contraception for up to 120 hours after unprotected intercourse and find that it can still be effective in some cases, even after 72 hours.

The menstrual cycle is usually unaffected by the use of emergency contraception. Breast tenderness is variable. Significant nausea occurs in about half of women and vomiting affects in about one in 6 women. These symptoms generally disappear within a day or two and can be moderated by using any standard anti-emetic or anti-nausea drug starting an hour before the BCPs are taken. If started after the onset of symptoms, these medications are not likely to be effective.

The mechanisms by which this contraceptive effect occurs have not been established, but based on registry data, should a pregnancy occur despite the use of these BCPs, there is no evidence of harm to the fetus from having been exposed.

Theories of how emergency contraception are many, but the single best explanation for its mechanism of action is the disruption or inhibition of normal ovulation. Historically, there has been a concern that emergency contraception might act by causing early pregnancy losses, but many studies have shown that not to be the case. Once ovulation has occurred, emergency contraception with combination birth control pills does not seem to have any measurable effect on the menstrual cycle, fertilization, implantation, or growth and development of the fetus.

Contraindications to use of emergency contraception are essentially the same as those for use of the birth control pill in general. Previous stroke, undiagnosed uterine bleeding, heart attack, deep vein thrombophlebitis and cancer of the breast or uterus are all contraindications to sustained pill use. The extent to which they represent risks in the context of emergency contraception is not known, but should be weighed in evaluating a patient for emergency contraceptive use.

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