An intrauterine device (IUD) is a type of long-acting birth control. It’s a small device that your doctor can put into your uterus to prevent pregnancy. There are two main types: copper IUDs (ParaGard) and hormonal IUDs (Kyleena, Liletta, Mirena, Skyla).

Both types of IUD are more than 99 percent effective at preventing pregnancy, according to Planned Parenthood. Over the course of a year, fewer than 1 out of 100 women with an IUD will get pregnant. That makes it one of the most effective forms of birth control.

In very rare cases, it’s possible to get pregnant while using an IUD. If you do get pregnant while using an IUD, you’re more likely to have an ectopic pregnancy or miscarriage. But your overall risk of experiencing these complications is low.

Ectopic pregnancy happens when a pregnancy develops outside your uterus. For example, it can happen if a fertilized egg starts to grow in your fallopian tube.

Ectopic pregnancy is rare but serious. If left untreated, it can cause internal bleeding and infection. In some cases, it can even be fatal.

If you get pregnant while using an IUD, the device raises the chances that your pregnancy will be ectopic. But if you have an IUD, your risk of getting pregnant in the first place is low. In turn, your overall risk of ectopic pregnancy is also low.

According to scientists in the , ectopic pregnancy affects an estimated 2 out of 10,000 women with a hormonal IUD each year. It affects an estimated 5 out of 10,000 women with a copper IUD each year.

In comparison, more than 1 out of 100 sexually active women who don’t use birth control will have an ectopic pregnancy over the course of a year.

A miscarriage happens if a pregnancy ends spontaneously before its 20th week. At that point, the fetus isn’t developed enough to survive outside the uterus.

If you get pregnant while using an IUD, the device increases the risk of miscarriage. If you want to stay pregnant, it’s important to remove the IUD early in pregnancy.

Sometimes, an IUD can slip out of place. If that happens, the risk of pregnancy is higher.

To check the placement of your IUD:

  1. Wash your hands with soap and water.
  2. Get into a comfortable sitting or squatting position.
  3. Insert your index or middle finger into your vagina. You should be able to feel the string attached to your IUD, but not the hard plastic of the IUD itself.

Contact your doctor if:

  • you can’t feel the IUD string
  • the IUD string feels longer or shorter than it used to
  • you can feel the hard plastic of the IUD coming out of your cervix

Your doctor can use an ultrasound exam to check the internal positioning of your IUD. If it has slipped out of place, they can insert a new IUD.

An IUD can work for years before you need to replace it. But eventually it expires. Using an expired IUD may raise your risk of pregnancy.

In most cases, a copper IUD can last for up to 12 years. A hormonal IUD can last for up to 3 years or longer, depending on the specific brand you use.

Ask your doctor when you should have your IUD removed and replaced.

The birth control effects of an IUD are completely reversible. If you want to get pregnant, you can remove your IUD at any time. After you remove it, you can try to get pregnant right away.

If you have an IUD, contact your doctor if you:

  • want to become pregnant
  • think you might be pregnant
  • suspect that your IUD has slipped out of place
  • want to have your IUD removed or replaced

You should also contact your doctor if you develop any of the following signs or symptoms while using an IUD:

  • fever, chills, or other signs of infection
  • bad pain or cramps in your lower belly
  • unusual discharge or heavy bleeding coming from your vagina
  • pain or bleeding during sex

In most cases, the potential side effects of using an IUD are minor and temporary. But in rare cases, an IUD can cause serious complications, such as:

  • ectopic pregnancy
  • bacterial infection
  • perforated uterus

An IUD is a highly effective method of birth control. But in rare cases, it’s possible to get pregnant while using it. If that happens, you’re at risk of having an ectopic pregnancy or miscarriage. Talk to your doctor to learn more about the potential benefits and risks of using an IUD.