The IUCD/LNG-IUS inserted within 120 hours of unprotected intercourse is used as emergency contraception. Which mechanism accounts for the higher efficacy of copper IUCD over levonorgestrel (Plan B) as emergency contraception?

• A Copper IUCD inhibits ovulation more completely than levonorgestrel
• B Copper IUCD releases high-dose levonorgestrel locally in the endometrium
• C Copper ions directly inhibit sperm motility and viability and may prevent fertilisation, with a post-fertilisation effect as a backup ✓
• D Copper ions stimulate progesterone receptor blockade in the decidua

Explanation

The copper IUCD's superior emergency contraception efficacy (failure rate <0.1% vs 1–2% for LNG) is due to: (1) primary mechanism — copper ions impair sperm motility and function, reducing fertilisation probability (pre-fertilisation effect); (2) if fertilisation occurs, the inflammatory endometrial environment and altered uterine secretions impair implantation (post-fertilisation effect). The copper IUCD is also effective even when inserted up to 5 days after the calculated ovulation date, unlike LNG which must be taken before ovulation. It does not suppress ovulation like ulipristal acetate.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

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Written and medically reviewed by the StethoPrep medical team.