No method of birth control is perfect, but the intrauterine device (IUD) is one of the most effective ways to prevent pregnancy. The risk of getting pregnant when an IUD is in place is less than 1%.

Another advantage of the IUD, compared to other birth control options, is convenience. Once it is placed, the woman does not need to do anything for it to work.

There are two different IUDs available in the United States. Both are small plastic devices. One contains copper (ParaGuard). The other contains a progesterone-like hormone (Mirena). The ParaGuard device lasts up to 12 years. The Mirena type is changed after five years. The hormone in the Mirena acts within the uterus. Very little of the progestin gets into the bloodstream. The hormone also decreases cramps and menstrual bleeding.

The IUD does not prevent sexually transmitted diseases (STDs). It is not a good choice for women who are at increased risk for STDs. This includes women who have had a prior pelvic infection and those who are not in mutually monogamous relationships. The IUD should not be used in women who have an abnormally shaped uterine cavity.

When pregnancy does occur in a woman using an IUD, there is a chance that it is an ectopic pregnancy. An ectopic pregnancy is a potentially dangerous situation in which the pregnancy starts to develop outside of the uterus, usually within the fallopian tube. This is a rare complication, but it highlights how important it is for all IUD users to call their doctor or gynecologist if they experience lower abdominal or pelvic pain or a new vaginal discharge.