A single-arm study to evaluate the efficacy, safety and acceptability of pericoital oral contraception with levonorgestrel

BackgroundAn oral dose of 0.75 mg levonorgestrel (LNG) taken shortly after sex was marketed as a routine, nonemergency contraceptive method until the 1990s. Because a hormonal method used only at the time of intercourse may be desirable for women who have infrequent sex, we conducted a study to reevaluate the potential of pericoital LNG as a primary means of contraception.MethodsWe enrolled women aged 18-45 years in Brazil and the USA who expected to have sex 1-4 days per month for 6.5 months. Participants were instructed to take one tablet 0.75 mg LNG within 24 h before or after sex, with no more than one dose in any 24-h period. The primary efficacy measure was the Pearl Index among women aged 18-35 years.ResultsThe study was stopped after 72 of the planned 300 participants were enrolled due to slow recruitment and related feasibility considerations. In the primary analysis, three pregnancies occurred during 13.4 woman-years of follow-up, resulting in a Pearl Index of 22.4 (95% confidence interval, 4.6-65.4). No serious adverse events were reported, and vaginal bleeding patterns were generally acceptable.ConclusionsOur estimated Pearl Index was noticeably higher than expected from previous research of LNG for pericoital contraception. Although the regimen was safe and generally acceptable, the study was challenged by slow enrollment and curtailed person-years of follow-up, resulting in poor precision for the estimated treatment effect. Future research may inform whether our results are symptomatic of the regimen, study design or characteristics of the populations from which we recruited.ImplicationsOur study failed to confirm prior data suggesting that 0.75 mg LNG for pericoital contraception could be more effective than typical use of barrier methods among women having infrequent sex. Characterizing populations most likely to adhere to, and benefit from, pericoital regimens is essential to future research on these methods.