The letters IUD stand for “intrauterine device.” IUDs are small, “T-shaped” devices made of flexible plastic. A health  care provider inserts an IUD into a woman’s uterus to prevent pregnancy.

There are two brands of IUD available in the United States — ParaGard and Mirena.

ParaGard IUDThe ParaGard IUD contains copper. It is effective for 12 years.

Mirena IUDThe Mirena IUD releases a small amount ofprogestin, a hormone. It is effective for five years.

How Does an IUD Work?

Both the ParaGard and the Mirena IUDs work mainly by affecting the way sperm move so they can’t join with an egg. If sperm cannot join with an egg, pregnancy cannot happen.

For some women, Mirena may prevent the egg from leaving the ovary. Pregnancy cannot happen if there is no egg to join with sperm. Progestin also prevents pregnancy by thickening a woman’scervical mucus. The mucus blocks sperm and keeps it from joining with an egg.

How Effective Is the IUD?

Effectiveness is an important and common concern when choosing a birth control method. IUDs are one of the most effective forms of birth control available. Less than 1 out of 100 women will get pregnant each year if they use the ParaGard or the Mirena IUD.

Keep in mind that the IUD doesn’t protect against sexually transmitted infections. Use a latex or female condom along with the IUD to reduce the risk of infection.

How Safe Is the IUD?

Most women can use either the ParaGard or the Mirena IUD safely. But all medications have some risks, so safety is a common concern when choosing a birth control method. Certain conditions increase the risk of side effects. Talk with your health care provider about your health and whether an IUD is likely to be safe for you. There are many other methods of birth control that may be safe for you if you cannot use an IUD.

You should not use an IUD if you

  • have had a pelvic infection following either childbirth or an abortion in the past three months
  • have or may have a sexually transmitted infection or other pelvic infection
  • think you might be pregnant
  • have cervical cancer that hasn’t been treated
  • have cancer of the uterus
  • have unexplained bleeding in your vagina
  • have pelvic tuberculosis
  • have a uterine perforation during IUD insertion

How Is an IUD Removed?

Having an IUD removed or replaced is usually simple. Your health care provider will do it for you. Women should never try to remove IUDs themselves or ask nonprofessionals to do it for them. Serious damage could result.

In rare cases, IUDs cannot be easily pulled free. In these cases, the cervix may have to be dilated and a surgical tool may be used to free the IUD. In very rare cases, surgery becomes necessary.