IUDs which are used by females:
(1) Are implanted under the skin and they release progestogen and estrogen
(2) Act as spermicidal jellies
(3) Release copper ions in the uterus that increase phagocytosis of sperm
(4) Block the entry of sperms into vagina.
(3) IUDs increase phagocytosis of sperms within the uterus and the Cu ions releases suppress sperm motility and the fertilising capacity of sperms. The hormone releasing IUDs make the uterus unsuitable for implantation and the cervix hostile to the sperms. (page-60)