Emergency Contraception: Efficacy Difference between Levonorgestrel and Ulipristal Acetate According to Follicle Size at the Time of Unprotected Sexual Intercourse

The most frequently used treatment worldwide for emergency contraception is the levonorgestrel (LNG) pill. However, its efficacy decreases if it is administered 3 days after unprotected sexual intercourse, whereas the ulipristal acetate (UPA) pill is effective up until 5 days afterwards. Pooled clinical data show that UPA is more effective than LNG when taken very shortly after intercourse (within 24 h) or, conversely, between 72 and 120 h after intercourse. UPA is also more effective than LNG in inhibiting follicular rupture when administered near the time of ovulation. We show here why overall UPA is more effective than LNG in reducing the rate of unwanted pregnancies by demonstrating the effect of each product according to follicle size at the time of unprotected sexual intercourse We also explain the difference between UPA and LNG in the maximum time to administration simply by the shift in ovulation and the fact that UPA has an effect on larger follicles than LNG (18 mm vs. 14 mm), without postulating a hypothetical endometrial effect. We also explain why UPA and LNG remain emergency contraceptives and should not be used for daily contraception.