What Are IUDs?

The letters “IUD” stand for “intrauterine device.” When placed inside a woman’s uterus, an IUD helps prevent pregnancy. The IUD is considered the most cost effective long-term reversible method of contraception available in the world.

IUDs are small devices made of flexible plastic in the shape of a “T.” There are two types of IUDs available in the U.S.:

  • ParaGard Copper T 380A contains copper and can be left in place for 10 years.
  • Mirena contains the hormone levonorgestrel and must be replaced every 5 years.

Once inserted, the IUD is immediately effective. When removed, its contraceptive effect is immediately reversed.

How Do IUDs Work?

IUDs usually prevent fertilization of the egg. Scientists are not entirely sure how. IUDs seem to affect the way the sperm or egg moves. It may be that substances released by the IUD immobilize sperm. Another possibility is that the IUD prompts the egg to move through the fallopian tube too fast to be fertilized.

The copper in the ParaGard Copper T adds to the effectiveness of the IUD in two other ways. It affects the behavior of enzymes in the lining of the uterus to prevent implantation. It also causes the production of increased amounts of prostaglandin, the hormones that support pregnancy.

The Mirena works by delivering a very small amount of progestin directly on the inner wall of the uterus. This dose is approximately the same dose as taking two or three mini-pills a week. The progestin may prevent pregnancy by thickening the cervical mucus, which makes it difficult for sperm to get through to fertilize the egg, inhibiting the normal sperm movement inside the uterus and ovarian tubes and reducing the growth of the lining of the uterus.

How Effective is the IUD?

  • ParaGard Copper T: over 99% effective
  • Mirena: over 99% effective

What are the Side Effects?

  • Cramping within the first few days of insertion
  • May experience more spotting and irregular periods within the first few months
  • With the ParaGard women may experience longer, heavier periods
  • With the Mirena women may have lighter and fewer periods over time