Contraception is the use of hormonal or non-hormonal methods to prevent pregnancy. It can work through one or more mechanisms, including stopping an egg maturing, stopping sperm reaching or fertilising an egg, or preventing implantation of an embryo. Methods that stop sperm and egg from meeting include condoms, spermicide, and sterilisation: vasectomy blocks the sperm ducts, while female sterilisation blocks the oviducts. The copper IUD primarily prevents fertilisation by releasing copper ions that impair sperm movement and function.