Ulipristal acetate prevents ovulation more effectively than levonorgestrel: analysis of pooled data from three randomized trials of emergency contraception regimens.

The days just prior to ovulation are the most crucial for emergency contraception (EC) efficacy. Ulipristal acetate (UPA) and levonorgestrel's (LNG) capacity to inhibit follicular rupture have never been compared directly at this time of the cycle.