"IUD" stands for "intrauterine device," a plastic, T-shaped contraceptive device that helps to prevent pregnancy, according to WebMD. Copper IUDs are wrapped in copper wire that creates a toxic liquid that kills sperm. Hormonal IUDs contain hormones that kill sperm and thicken the cervical mucus, preventing sperm penetration.
Intrauterine devices must be inserted by a health care specialist and can prevent pregnancy for up to 12 years, states Planned Parenthood. IUDs do not protect women against sexually transmitted diseases, so it is important to use condoms along with IUDs for additional protection. When used properly, IUDs are an effective mode of birth control with an approximate yearly success rate of over 99 percent.