Which oral emergency contraceptive option acts as an antiprogestin that delays follicular rupture?

Ulipristal is an oral emergency contraceptive that functions as an antiprogestin, specifically by delaying follicular rupture. It works primarily by blocking the effects of progesterone, which is crucial for ovulation. By doing so, it can prevent the ovary from releasing an egg, thus reducing the chances of fertilization if taken during the menstrual cycle.

Ulipristal's effectiveness lasts longer than some other options, allowing it to be used up to 120 hours (5 days) after unprotected intercourse, which is a significant advantage. In contrast to other emergency contraceptive methods, such as levonorgestrel or Plan B, which are mainly progestin-based and primarily work by preventing ovulation when taken before the luteinizing hormone surge, ulipristal provides a different mechanism that can be effective even when taken closer to ovulation.

Mifepristone, while also an antiprogestin, is primarily used for medical abortion and not for emergency contraception, making it unsuitable for this specific question. Thus, ulipristal's role as a delay to follicular rupture distinguishes it as the correct answer.