July 1996

The Yuzpe regimen of emergency contraception: How long after the morning after?

Trussell J, Ellertson C, Rodriguez G. The Yuzpe regimen of emergency contraception: How long after the morning after? Obstetrics & Gynecology. 1996 Jul;88(1):150-4

Objective: To determine whether failure of the Yuzpe method of emergency contraception (which involves taking a higher than usual dose of ordinary combined oral contraceptives within 72 hours after unprotected intercourse, with a second dose taken 12 hours later) depends on the interval between intercourse and treatment.

Data Sources: We searched the literature for studies in which investigators separately reported both the number of women treated with the Yuzpe regimen and the resulting pregnancies when treatment was started on the first, second, and third days after unprotected intercourse. Searches of the electronic data bases MEDLINE, POPLINE, EMBASE, and BIOSIS were supplemented by scrutiny of the bibliographies of all papers identified through the electronic search.

Methods of Study Selection: We identified nine published studies that present the number of women treated and outcome of treatment by time since unprotected intercourse. We included all nine studies in our analysis.

Tabulation, Integration, and Results: Differences in failure rates by time of treatment adjusted for study-site effects were analyzed using logistic regression. We found no significant differences in failure rates when therapy was started on the first, second, or third day after unprotected intercourse. The large sample size ensured a power of 76% to reject the null hypothesis of equal failure rates when the odds of failure on the third day are twice those on the first and second days.

Conclusion: Our results have two clinical implications. First, insistence on taking the first dose as soon as possible may be counterproductive in circumstances when taking the second dose 12 hours later would be difficult. Second, clinical protocols that deny treatment after 72 hours may be excessively restrictive, particularly if the alternative of emergency insertion of a copper intrauterine device is not immediately available or appropriate.