An intrauterine device is a highly effective, small, T-shaped birth control device made of flexible plastic and copper. It is inserted into the uterus to prevent pregnancy.

Fewer than 1 in 100 women become pregnant with an intrauterine device (IUD) in place, according to Planned Parenthood.

The device has a polyethylene string attached to it. The string allows a means of checking to see if the IUD is still in place, as they occasionally can slip out. It enables a doctor to remove the device easily when it needs changing or is no longer wanted.

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An IUD can be copper or hormone-based. In the United States (U.S.) the usual available brands are ParaGard, Mirena, Liletta, Kyleena, and Skyla.

ParaGard is a copper IUD that works by providing an unfavorable environment for sperm, fertilization, and implantation.

The others are all hormonal IUDs, and they prevent pregnancy by releasing hormones.

An IUD is normally used as a long-term birth control method, but a copper IUD can also reduce the risk of unintended pregnancy by up to 99.9 percent if it is inserted within 120 hours following unprotected intercourse.

With a copper IUD, protection begins as soon as the device is fitted. A hormonal IUD provides immediate protection, as long as it is inserted within 7 days after the first day of a period.

If it is not inserted during that timeframe, protection will not begin until 7 days after insertion. It is necessary to use a backup method of birth control, such as condoms or spermicide, will be necessary.

Mirena can remain within the uterus and prevent pregnancy for 5 years. Skyla, another hormonal IUD, remains effective for up to 3 years.

The different types release different quantities of hormones each day, and the amount decreases over time.

ParaGard can remain within the uterus and provide protection for 10 years after insertion. It is approved for 10 years, but studies have shown it can be effective for up to 20 years, in some cases.

A hormonal IUD releases a type of progestin that is responsible for the thickening the cervical mucus. It prevents conception by stopping the sperm from being able to reach an egg. It also partially suppresses ovulation.

The non-hormonal IUD does not release a hormone. Instead, the copper coil within the IUD produces an inflammatory or immune response in the uterus. This unfavorable environment for sperm will reduce the chances of fertilization and prevent implantation.

As a form of birth control, the IUD:

  • is cost-effective, as the device lasts for 3 to 12 years, depending on the type
  • allows spontaneity during sex, without having to worry about pregnancy
  • can be used while breastfeeding
  • allows for pregnancy immediately after removal

A copper IUD, being non-hormonal, does not affect hormone levels in the body.

The hormonal options can mean lighter and less painful menstrual cramps, but they can lead to ovarian cysts, mood changes, and acne.

Possible problems

Possible disadvantages or side effects of having an IUD include:

  • spotting of blood between periods for 3 to 6 months
  • irregular menses for 3 to 6 months with a hormonal IUD
  • heavy periods with worsened cramps with a copper IUD
  • the IUD can partially or fully fall out, so at the end of each period a woman should insert a finger and feel for the string, to ensure the IUD has not been passed with the period
  • use of a copper IUD can lead to anemia, because of heavier periods
  • IUDs can increase the chance of an ectopic pregnancy
  • IUDs do not protect from sexually transmitted infections (STI), and condoms should also be used when needed for protection
  • IUDs are a foreign object in the uterus, and this can increase the risk of getting an STI or other infection such as pelvic inflammatory disease

Rarely, an infection can occur, or the IUD can push through the uterine wall. The IUD cannot get lost or travel around inside the body.

If pregnancy occurs while an IUD is in place, there is a higher risk that it will be ectopic, or that a pelvic infection, a miscarriage, or premature labor and delivery will occur. However, a healthy pregnancy and baby can also result.

If a pregnancy occurs with an IUD in place, the doctor will monitor the pregnancy more closely.

For most women, an IUD is a safe and effective method of birth control, but it is not suitable for everyone.

Women who may not be able to use an IUD include those who:

  • have had a pelvic infection after childbirth
  • have had an abortion within the last 3 months
  • have or may have a sexually transmitted infection (STI) or pelvic infection
  • may be pregnant
  • have untreated cervical cancer or uterine cancer
  • are experiencing unexplained vaginal bleeding
  • have multiple different partners, due to a high risk of infection
  • have a history of pelvic tuberculosis or uterine perforation at the time of an IUD insertion

The Association of Reproductive Health Professionals (ARHP) argue that an IUD can be safely used in women who have just had an abortion, and those with a history of an STI or pelvic inflammatory disease (PID), but that decision will depend on the doctor and the individual’s medical history.

They also say that it safe for use by:

  • teens
  • women who have never given birth
  • women with a history of ectopic pregnancy

A copper IUD is not suitable for a woman who has an allergy to copper or a history of Wilson’s disease.

Hormonal IUDs should not be used with severe liver disease or if a woman has or could have breast cancer.

Each woman should discuss their medical history with a health care provider to determine if an IUD is suitable, and, if so, which type.

Before fitting an IUD, a medical professional will carry out a physical examination to check for infections or other issues.

They may offer a local anesthesia, as insertion can be painful for some women.

To fit the device, the health care provider will insert a speculum into the vagina and then, using a special inserter, they will put the IUD through the cervix an into the uterus.

This normally takes about 5 minutes.

There may be some pain or cramping during insertion and for a few minutes after. Some dizziness may occur.

Recovery can be almost immediate, but some women experience cramping discomfort for the rest of the day. Heating pads and over-the-counter (OTC) pain killers can help.

Cramping and spotting may continue intermittently for 3 to 6 months. This is normal. If it gets worse, medical help should be sought.

A woman who has an IUD fitted should notify their doctor immediately if:

  • there is a change in length of the IUD string, or she cannot locate the string
  • the plastic portion of the IUD can be felt when feeling the cervix
  • she may be pregnant
  • menses are heavier or longer after insertion than before
  • there is severe abdominal cramping, pain, or abdominal tenderness
  • pain and or bleeding occur with intercourse
  • there are signs of infection, including fever, chills, flu-like symptoms, muscle aches, and tiredness
  • an abnormal or foul-smelling vaginal discharge occurs
  • she has an unusually light period, a missed or late period, or unexplained vaginal bleeding

In 2014, experts recommended advising all women of a slightly higher risk of developing PID within the first 20 days after fitting.

Some insurance companies cover the cost of an IUD. It is worth asking the doctor beforehand if your insurance will cover it.