The letters "IUD" stand for "intrauterine device."
IUDs are small, "T-shaped" contraceptive devices made of flexible plastic. IUDs are available by prescription only. A woman and her clinician decide which is the right type for her, and the clinician inserts it in her uterus to prevent pregnancy. Two types are now available in the U.S.:
ParaGard (Copper T 380A) contains copper and can be left in place for 12 years
Mirena continuously releases a small amount of the hormone progestin, and is effective for five years
How IUDs Work
Both kinds of IUDs work by preventing sperm from joining with an egg by affecting the way they move. The hormone in Mirena increases effectiveness. It thickens cervical mucus, which provides a barrier that prevents sperm from entering the uterus. It also prevents some women's ovaries from releasing eggs (ovulation).
IUDs also alter the lining of the uterus. In theory, this may prevent pregnancy by preventing the implantation of a fertilized egg but this has not been scientifically proven.
IUDs have a string attached that hangs down through the cervix into the vagina. A woman can make sure the IUD is in place by feeling for the string in her vagina. A clinician uses the string to remove the IUD.
Effectiveness
The IUD is one of the most effective reversible methods of birth control. Of 100 women who use ParaGard or Mirena, one or fewer will become pregnant during the first year of typical* use. Fewer than one will become pregnant with perfect** use. Fewer pregnancies occur with continued use.
It is very important to remember that the IUD does not protect against sexually transmitted infections. Use a latex or female condom with the IUD to reduce the risk of infection.
*Typical use refers to failure rates for women whose use is not consistent or always correct.
**Perfect use refers to failure rates for those whose use is consistent and always correct.
Advantages
IUDs are the most popular form of