The IUD (intrauterine device) is a piece of plastic coated with copper that is inserted within the uterus by a doctor. Copper is then gradually released (IUD may last 5 to 10 years) and since it has a spermicidal action sperm cells are destroyed before fecundation. Besides this mechanism the movement of the IUD inside the uterus causes slight endometrial inflammation that helps to prevent nidation.