Is the IUD an abortifacient?
Some people incorrectly believe that the principal mechanism of action of IUDs is prevention of implantation of fertilized eggs.16 The existing evidence does not support the theory that the mechanism of action of IUDs includes the destruction of embryos in the uterus. The foreign body reaction induced by copper and inert IUDs is hostile to sperm and possibly eggs in the upper genital tract. Few sperm reach the site of fertilization in the fallopian tubes, and those that do are unlikely to be capable of fertilizing an egg. Eggs may be similarly impaired. Should fertilization occur, the chances for establishing a pregnancy likely decrease as the fertilized egg approaches the uterine cavity. Thus, the IUD appears to work at a much earlier stage of human reproduction than was previously thought; prevention of fertilization seems to be the dominant mode of action. As noted by the World Health Organization Scientific Group:17 “It is unlikely that the contraceptive efficacy of IUDs results, m
