Review Question - QID 107201

This patient has been prescribed a combined estrogen/progestin emergency contraception. The most likely mechanism of action is inhibition or delay of ovulation.

Combined estrogen/progestin contraception, also known as the Yuzpe method, is an effective form of postcoital contraception when taken within 72 hours of sexual intercourse. Numerous clinical studies have demonstrated that combined estrogen/progestin contraception inhibits or delays ovulation. Recent studies have demonstrated that alteration of the endometrium is not a mechanism of action for combined contraception.

Bosworth et al. review emergency contraception options. The combined oral contraception requires a physician prescription, which may deter some patients from seeking this option. Levonorgestrel as a 1.5 mg single dose, also known as Plan B, can be obtained over-the-counter without any age restrictions. It has been shown to be slightly less effective than combined contraception (79% compared to 86%). A copper IUD, the most effective emergency contraception (99.9% success rate), may be placed up to 7 days after intercourse.

Glasier et al. performed a meta-analysis of two randomized controlled trials to identify potential risk factors for failed emergency contraception. They found that overweight women (BMI between 25 and 30) had a 1.5 greater risk of emergency contraception failure and that obese women (BMI greater than 30) had a more than 3 times greater risk of emergency contraception failure. They recommended that a copper IUD may be the best option for overweight and obese women seeking emergency contraception.

Incorrect Answers:
Answer 2: Recent clinical studies have shown that alteration of the endometrium is not a physiological response to combined estrogen/progestin emergency contraception.
Answers 3-5: There is no clinical data supporting these mechanisms of action for the combined estrogen/progestin emergency contraception.