What Is an Intrauterine Device?

The first copper IUD was introduced in 1971. Unfortunately, it was poorly designed, and over 100 women had spontaneous septic abortions. It was removed from the market at the urging of the FDA in 1974. Other copper IUDs came out in the mid-1970s but were not widely used in the U.S., possibly due to safety concerns by the general public. American suspicion of these devices seems to have persisted; in the 1990s, a survey showed that only 1.5 percent of North American women used them, as opposed to 18 percent of women in Scandinavia and 33 percent of women in Russia and China. Britain has 10 different brands of copper IUDs, whereas the U.S. has only one. Called Paragard, it was first approved by the FDA in 1984. The first IUD containing progesterone was developed in 1976. Called Progesterat, it released progesterone at 65 mcg per day and had to be replaced annually. It had a failure rate of 2 percent and was manufactured until 2001. Mirena, which is the hormonal IUD currently available in the U.S., was available in Europe in 1990, but not approved by the FDA until 2000. It releases 20 mcg per day of levonorgestrel, a progestin.

Both Mirena and Paraguard are small, T-shaped devices that are fitted into the uterus by a doctor.

Both IUDs cause the endometrium to release white blood cells and prostaglandins, creating a hostile environment for sperm and eggs. This makes it difficult for the sperm and egg to move through the reproductive tract and join together. They also change the cervical mucus, making it less likely that the sperm will enter the uterus. In Paraguard, the presence of copper also has a spermicidal effect. Mirena contains the hormone levonorgestrel, a common ingredient in oral contraception. Mirena may stop ovulation entirely.

Paraguard has a failure rate of 0.6 percent and can be used continuously for 10 years, and Mirena has a failure rate of 0.2 percent and can be used for up to 5 years. Though they have a higher upfront cost and require a doctor visit for placement, IUDs are very economical in the long run, as no further birth control costs are incurred for 5 or 10 years. Mirena is less likely to cause hormonal side effects, like breast tenderness, than some oral contraception. It does not cause weight gain. Mirena also reduces menstrual flow by up to 90 percent and may stop menstruation completely.

Paraguard can cause heavy menstrual bleeding and increased pain and discomfort. Mirena appears to increase the risk for benign ovarian cysts, though they rarely require treatment. There is also a small risk of uterine perforation, particularly during insertion. The device may be accidentally expelled, necessitating another doctor's visit for placement. Though the risk of ectopic pregnancy is less than for women who do not use birth control, women using IUDs are more likely to have an ectopic pregnancy than women who use other forms of birth control. Women who have an STD or get one while using an IUD are at an increased risk for pelvic inflammatory disease. IUDs do not provide any protection against STDs.