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Mechanism of action Although the precise mechanism of action is not known, currently available IUCs work primarily by preventing sperm from fertilizing ova.26 IUCs are not abortifacients: they do not interrupt an implanted pregnancy.27 Pregnancy is prevented by a combination of the "foreign body effect" of the plastic or metal frame and the specific action of the medication (copper or levonorgestrel) that is released. Exposure to a foreign body causes a sterile inflammatory reaction in the intrauterine environment that is toxic to sperm and ova and impairs implantation.28,29 The production of cytotoxic peptides and activation of enzymes lead to inhibition of sperm motility, reduced sperm capacitation and survival, and increased phagocytosis of sperm.30,31 The TCu380A causes an increase in copper ions, enzymes, prostaglandins, and white blood cells (macrophages) in uterine and tubal fluids; these impair sperm function and prevent fertilization. p. 162: Table 7-1. Myths and misconceptions about IUCs Myth: IUCs are abortifacients. Fact: IUCs prevent fertilization and are true contraceptives.
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