A woman requesting emergency contraception presents 96 hours after unprotected intercourse. A copper intrauterine device (Cu-IUD) is discussed. What is the proposed mechanism by which the Cu-IUD prevents implantation when used as emergency contraception?

• A Copper ions inhibit endometrial DNA synthesis, preventing decidualisation
• B Copper ions are spermicidal (by inhibiting sperm motility and acrosome reaction) and also cause a foreign body inflammatory endometrial response that is hostile to implantation ✓
• C Copper ions chelate progesterone receptors in the endometrium, preventing implantation
• D The IUD string causes cervical canal obstruction preventing sperm ascent

Explanation

The Cu-IUD exerts its contraceptive/emergency contraceptive effect through multiple mechanisms: copper ions are directly toxic to sperm (inhibiting motility and disrupting the acrosome reaction required for fertilisation), and the IUD creates a sterile foreign body inflammatory response in the endometrium characterised by prostaglandin release, leukocyte infiltration, and altered endometrial glycoproteins — this hostile environment impairs implantation even if fertilisation has occurred. The Cu-IUD is the most effective form of emergency contraception (>99.9%) and can be inserted up to 5 days after intercourse.

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

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