What is an IUD and How Do They Work?

Intrauterine devices (IUDs), also known as the coil, are small devices placed in the uterus to interrupt the process of insemination. They’re very popular around the world and one of the most effective forms of birth control.

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

An IUD releases copper to stop you getting pregnant and protects against pregnancy for between five and 10 years.


Facts about the IUD

  • When inserted correctly, IUDs are more than 99% effective
  • An IUD works as soon as it’s inserted and lasts for five to 10 years, depending on the type
  • It can be inserted at any time during your menstrual cycle, as long as you’re not pregnant
  • It can be taken out at any time by a specially trained doctor or nurse. It’s then possible to get pregnant straight away
  • Your periods can be heavier, longer or more painful in the first three to six months after an IUD is put in. You might get spotting or bleeding between periods
  • There’s a small risk of getting an infection after it’s been fitted
  • There’s a small risk that your body may push out the IUD or it may move. Your doctor or nurse will teach you how to check it’s in place
  • It can be uncomfortable when the IUD is put in, but painkillers can help
  • It may not be suitable if you have had previous pelvic infections
  • It does not protect against sexually transmitted infections (STIs), so you may need to use condoms as well


How it works

The IUD is similar to the intrauterine system (IUS), but instead of releasing the hormone progestogen like the IUS, the IUD releases copper into the womb.

The copper alters the cervical mucus, which makes it more difficult for sperm to reach an egg and survive. It can also stop a fertilised egg from being able to implant itself.

If you’re 40 or over when you have an IUD fitted, it can be left in until you reach the menopause or you no longer need contraception.


Having an IUD fitted

An IUD can be fitted at any time during your menstrual cycle, as long as you’re not pregnant. You’ll be protected against pregnancy straight away.

Before your IUD is fitted, a GP or nurse will check inside your vagina to check the position and size of your womb. You may be tested for any existing infections, such as STIs, and be given antibiotics.

The appointment takes about 20 to 30 minutes, and fitting the IUD should take no longer than five minutes:


Having an IUD fitted can be uncomfortable, and some people might find it a little painful, but you can have a local anaesthetic to help. Discuss this with a GP or nurse beforehand.

Let the person fitting your IUD know if you feel any pain or discomfort while you are having it fitted. You can ask them to stop at any time.

You can also take painkillers after having an IUD fitted if you need to.

You may get period-type cramps afterwards, but painkillers can ease the cramps. You may also bleed for a few days after having an IUD fitted.

Once an IUD has been fitted, it’ll need to be checked by a GP after three to six weeks to make sure everything is fine. Tell the GP if you have any problems after this initial check or if you want the IUD removed.

See a GP if you or your partner are at risk of getting an STI, as this can lead to an infection in the pelvis.

You may have an infection if you:

  • have pain in your lower abdomen
  • have a high temperature
  • have a smelly discharge


How to tell if it’s still in place

An IUD has two thin threads that hang down a little way from your womb into the top of your vagina.

The GP or nurse that fits your IUD will teach you how to feel for these threads and check that it’s still in place.

Check your IUD is in place a few times in the first month and then after each period, or at regular intervals.

It’s very unlikely that your IUD will come out, but if you cannot feel the threads or think it’s moved, you may not be protected against pregnancy.

See a GP or nurse straight away and use additional contraception, such as condoms, until your IUD has been checked.

If you have had sex recently, you may need to use emergency contraception.

Your partner should not be able to feel your IUD during sex. If they can, see a GP or nurse for a check-up.

Who can use an IUD

Most women can use an IUD, including those who are HIV positive.

A GP or nurse will ask about your medical history to check if an IUD is suitable for you.

The IUD may not be suitable if you:

think you might be pregnant

have an untreated STI or a pelvic infection

have problems with your womb or cervix

have unexplained bleeding between periods or after sex

Women who have had an ectopic pregnancy or who have an artificial heart valve must consult their GP or clinician before having an IUD fitted.


Advantages and disadvantages of the IUD

Although an IUD is an effective method of contraception, there are some things to consider before having one fitted.



It protects against pregnancy for 5 or 10 years, depending on the type.

Once an IUD is fitted, it works straight away.

Most women can use it.

There are no hormonal side effects, such as acne, headaches or breast tenderness.

It does not interrupt sex.

It’s safe to use an IUD if you’re breastfeeding.

It’s possible to get pregnant as soon as the IUD is removed.

It’s not affected by other medicines.

There’s no evidence that an IUD will affect your weight or increase the risk of cervical cancercancer of the uterus or ovarian cancer.



Your periods may become heavier, longer or more painful, though this may improve after a few months.

It does not protect against STIs, so you may need to use condoms as well.

If you get an infection when you have an IUD fitted, it could lead to a pelvic infection if not treated.

Most women who stop using an IUD do so because of vaginal bleeding and pain, although these side effects are uncommon.


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