Study Comparing Emergency Contraception Effectiveness in Women Who Weight ≥ 80 kg

Orally-dosed emergency contraception (EC) is highly effective when used properly. EC is up to 90% effective at preventing pregnancy following unprotected intercourse. Both ulipristal acetate (UPA) and levonorgestrel (LNG) delay or inhibit ovulation when used for EC. For individual women, use of EC provides a critical backup to prevent unintended pregnancy. However, obesity may severely impair EC effectiveness. Data from two large randomized control trials to identify risk factors for EC failure. A woman of obese body mass index (BMI) (≥30mg/kg2) using LNG-based EC had more than a 4 times greater risk of pregnancy compared to her normal BMI counterpart and a woman of overweight BMI (25-29.9) was at twice the risk of pregnancy. Failure was also associated with a high body weight. LNG-based EC appears to have a ceiling of efficacy at 70 kg and no efficacy for women 80 kg and above. It is believed that by doubling the dose to LNG 3.0 mg, serum levels of LNG are corrected to a therapeutic range.