What is the mechanism of action of levonorgestrel in emergency contraception?

• A. Preventing ovulation
• B. Thickening cervical mucus
• C. Altering the uterine lining
• D. Inhibiting sperm movement

Answer: (A)

Levonorgestrel, a synthetic progestin, primarily functions as an emergency contraceptive by preventing ovulation. When taken within a specified time frame after unprotected intercourse, it inhibits or delays the release of an egg from the ovary. This mechanism is crucial because if ovulation does not occur, there is no egg available for sperm to fertilize, thus effectively preventing pregnancy.

While levonorgestrel may also have secondary effects, such as thickening cervical mucus or altering the uterine lining, these are not its primary mechanisms of action in the context of emergency contraception. The thickening of cervical mucus makes it more difficult for sperm to navigate through the reproductive tract, and changes to the uterine lining can affect implantation; however, these functions are considered less direct in preventing pregnancy compared to the inhibition of ovulation itself. In terms of emergency contraception, the main goal is to prevent ovulation, making it the most relevant action for efficacy.