When screened for a hormone secreted just prior to implantation of a fertilized egg, one study found few IUD users who tested positive for the hormone. Copper accounts for this high degree of contraceptive efficacy, according to Irving Sivin, senior scientist at the Population Council, which developed the Copper T 380. But with copper, it is interfered with more. And the more copper, the more interruption. Copper IUDs also function well as emergency contraception when inserted within five days after unprotected intercourse.
Emergency contraception is used after unprotected coitus to avoid pregnancy.
Sarah Keller Footnotes Tredway DR, Umezaki CU, Mishell DR, et al. The mode of action of IUDs. Alvarez F, Brache V, Fernandez E, et al. New insights on the mode of action of intrauterine contraceptive devices in women. Wilcox AJ, Weinberg CR, Armstrong EG, et al.