Abstract
BACKGROUND: To explore why increased access to emergency contraception (EC) failed to reduce pregnancies in a recent randomized controlled trial. METHODS: We used multivariable logistic regression to identify risk factors for unintended pregnancy using data from a trial involving sexually active women (n = 1490, aged 14-24 years) randomly assigned to either increased access or standard access to EC. We used predictive modeling to generate estimated pregnancy risk scores for each participant. We then examined EC use among women at low or high baseline risk of pregnancy. RESULTS: Gravidity, recent history of unprotected sex (within 14 days of enrollment to study) and lower aversion to pregnancy predicted unintended pregnancy. Women in the increased access group were more likely than women in the standard access group to use EC repeatedly. This difference was significantly stronger (P = 0.03) among low risk women than high risk women [Relative risk (RR) 10.0, 95% confidence interval (CI) 6.5-15.4 and RR 5.5, 95% CI 3.8-7.9, respectively]. CONCLUSIONS: Increased access to EC had a greater impact on women who were at lower baseline risk of pregnancy. This may explain in part why increased access to EC has had no measurable benefit in clinical trials.