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What is the IUD?

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Updated December 14, 2003

What is the IUD?

An IUD is a T-shaped device inserted into the uterus by a healthcare professional. Three types of IUDs are available in the United States: the Paragard Copper T 380A; Progestasert Progesterone T; and the Mirena IUD. The Paragard IUD can remain in place for 10 years, while the Progestasert IUD must be replaced every year. The Mirena IUD is effective for up to five years.

The Mirena IUD works by delivering a very small amount of a progestin (20 mcg of levonorgestrel) directly on the inner wall of the uterus. It's not entirely clear how other IUDs prevent pregnancy. They seem to prevent sperm and eggs from meeting by either immobilizing the sperm on their way to the fallopian tubes or changing the uterine lining so the fertilized egg cannot implant in it.

IUDs have one of the lowest failure rates of any contraceptive method. "In the population for which the IUD is appropriate--for those in a mutually monogamous, stable relationship who aren't at a high risk of infection--the IUD is a very safe and very effective method of contraception," says Lisa Rarick, M.D., director of FDA's division of reproductive and urologic drug products.

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Adapted from the United States Office on Women's Health in the Department of Health and Human Services

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