What is an IUD? The IUD, also known as the intrauterine device, is a form of contraception that is a T-shaped plastic device that is placed inside the uterus to prevent implantation of a fertilized egg and the occurrence of pregnancy. The IUD is inserted by a doctor on demand and is reversible and protective. The function of the IUD is to prevent sperm from entering the uterus, or to prevent the fertilized egg from attaching to the endometrium after the sperm enters the uterus. The birth control ring achieves the contraceptive effect under the skin by releasing copper ions. Copper ions have inhibitory effects on the viscosity of cervical fluid, sperm motility, and the combination of sperm and eggs. Advantages of IUD