How does an IUD prevent pregnancy?

An Intrauterine Device (IUD) is a highly effective, long-lasting, and reversible form of birth control. It's a small, T-shaped device inserted into the uterus by a doctor. IUDs prevent pregnancy in a few ways: they create an environment in the uterus that's hostile to sperm, some release copper, which is toxic to sperm, and some thicken cervical mucus, making it difficult for sperm to reach the egg.