Healthwise

An intrauterine device, or IUD, is a small, T-shaped device that is inserted into the uterus to prevent pregnancy. It works by physically preventing sperm from reaching the egg. Some IUDs use copper as a sperm repellant while others use hormones to thicken mucus on the cervix to block sperm. IUDs do not stop ovulation from occurring. IUDs are over 99% effective, making them one of the most effective, reversible forms of birth control for women available.

IUDs have to be inserted in a doctor’s office, but once in place they will be effective for several years. The hormonal types of IUDs can be in place for 3 or 5 years and hormone-free type of IUD can stay in place up to 10 years. They're also safe to use if you’re breastfeeding, and can be removed at any time if you want to get pregnant in the future, without delaying your return to fertility. IUDs are very safe for most people, and side effects are rare and usually mild. While fewer than 1% of women get pregnant while using an IUD, those who do have a higher risk of miscarriage, ectopic pregnancy, and complications.

While IUDs can be an easy, safe, and effective way to prevent pregnancy, they don't protect against sexually transmitted infections, so you and your partner will need to use condoms or internal condoms to reduce your risk.