Intrauterine devices (IUDs) are small devices placed in your uterus to interrupt the process of insemination. IUDs have been on and off the market for decades. They’re very popular around the world and one of the most effective forms of birth control. Two to 8 in every 1,000 women who have IUDs get pregnant in a year of typical use.

There are two types of IUD: copper and hormonal. Currently, there are four brands of IUDs available in the United States: ParaGard is a copper IUD, and Mirena, Liletta, and Skyla are hormonal IUDs that use progestin.

IUDs are an excellent choice of birth control for many women. However, they are not the best choice for women who are at a high risk for sexually transmitted infections (STIs).

Both the copper and hormonal types of IUDs work by making it difficult for sperm to reach your egg.

ParaGard causes an inflammation response in the lining of your uterus. This inflammation is toxic to sperm. It also makes your uterus hostile to implantation, if fertilization occurs. But recent studies have failed to find evidence that fertilization ever occurs. ParaGard works for up to 10 years after it’s inserted.

Mirena works to thin the lining of your uterus to prevent the transport of sperm into your fallopian tubes where fertilization must occur. The progestin it releases also thickens your cervical mucus and can prevent ovulation. Mirena can last for up to five years after insertion. Skyla and Liletta are smaller and contain a lower dose of progestin. They both thin your uterus lining, and can last up to three years.

An IUD is inserted by a healthcare professional. Make an appointment with your doctor to determine if the IUD is the best birth control option for you. An IUD can be inserted any time it’s certain that you’re not pregnant.

Your doctor will insert the IUD through your cervix and into your uterus. The procedure usually takes less than 15 minutes. It can be done with or without local anesthesia. You’ll probably feel some cramping or discomfort.

There is a very small risk of expulsion when the IUD is implanted. For the first few months, it’s important to check that it’s still in place. You should do this every month.

To check your IUD:

  1. Wash your hands with soap and water.
  2. Put your finger into your vagina until you touch your cervix.
  3. Feel for the string ends.

You should be able to feel the string. If the string feels shorter or longer than normal, there may be a problem. You should not feel the hard end of the IUD against your cervix.

If there is a problem, don’t pull on the string or try to reinsert the IUD yourself. Instead, make an appointment with your doctor. While you’re waiting for the IUD to be reinserted, use an alternative form of contraception.

Expulsion is rare. If it happens, it will probably be during your period. Expulsion is most likely in the first few months after insertion.

Both types of IUDs are more than 99 percent effective at preventing pregnancy. They’re one of the most effective types of birth control available. They’re also one of the most convenient forms of birth control because they work for between 3 and 10 years.

An IUD has many benefits. Among them are:

  • effectiveness
  • longevity
  • convenience: IUDs don’t require preparation before sex
  • can be used while breastfeeding
  • quickly reversible if you want to get pregnant
  • inexpensive: After the initial cost of insertion, there are no more costs for 3 to 10 years

Mirena, Liletta, and Skyla can also help relieve:

  • menstrual pain
  • heavy periods
  • pain from endometriosis

ParaGard can also be used as a form of emergency contraception. According to Planned Parenthood, it is 99.9 percent effective at preventing a pregnancy if inserted within five days of unprotected intercourse.

As with any birth control method, there are pros and cons you’ll have to weigh before making your decision on which to use. IUDs have the following disadvantages:

  • they don’t protect against STIs
  • insertion can be painful
  • ParaGard may make your periods heavier
  • ParaGard may also make your menstrual cramps worse
  • Mirena, Liletta, and Skyla may make your periods irregular
  • they increase your chance of getting infections

These side effects usually go away within the first six months of use.

There is a risk of infection when you use an IUD. This risk is highest during insertion. You shouldn’t get an IUD if you have, or may have, an STI. In addition, IUDs are not recommended for women who:

  • might be pregnant
  • have untreated cervical cancer
  • have uterine cancer
  • have unexplained vaginal bleeding
  • have multiple sexual partners (due to increased risk for STIs)

ParaGard isn’t recommended for women who are, or might be, allergic to copper, or women who have Wilson’s disease. In rare situations, an IUD can penetrate the uterine wall. If pregnancy does occur with an IUD in place, there is increased risk to the pregnancy.

Mirena, Liletta, and Skyla aren’t recommended for women who have severe liver disease, or women who have, or may have, breast cancer.

Because there’s a slight risk of infection when your doctor inserts the IUD, they may test for STIs first.