An otherwise healthy 22-year-old woman requests the levonorgestrel emergency contraceptive pill (1.5 mg single dose). She had unprotected intercourse 72 hours ago. She weighs 80 kg. Which statement about efficacy at this weight is most accurate?
- A Efficacy is unaffected by body weight; pregnancy rate is less than 1%
- B Studies suggest significantly reduced efficacy in women over 75 kg; ulipristal acetate or Cu-IUD is preferred ✓
- C Doubling the LNG dose to 3 mg restores efficacy completely in obese women
- D LNG EC is contraindicated above 70 kg; a combined OCP should be used instead
Correct answer: B. Studies suggest significantly reduced efficacy in women over 75 kg; ulipristal acetate or Cu-IUD is preferred
Explanation
Pharmacokinetic studies and WHO-supported evidence show that levonorgestrel emergency contraception has significantly reduced efficacy in women weighing more than 75 kg, with possible complete failure above 80 kg. Ulipristal acetate (UPA-EC) maintains effectiveness up to 95 kg and is preferred. A copper IUD is the most effective emergency contraceptive regardless of weight. Doubling the LNG dose has insufficient evidence to restore efficacy.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
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Written and medically reviewed by the StethoPrep medical team.