IUS (intrauterine system): your guide

An IUS is a small T-shaped plastic device that is put into your uterus (womb). It releases a progestogen hormone. This is similar to the natural progesterone that women produce in their ovaries.

The IUS has two threads at one end which hang through the opening at the entrance of your uterus into the top of your vagina.

It works for up to five years. If you are aged 45 or older when the IUS is fitted, it can be left in until the menopause.

Read this information to find out:

• What is the difference between an IUS and an IUD?
• How effective is an IUS?
• When will an IUS start to work?
• How does an IUS work?
• What are the advantages of an IUS?
• What are the disadvantages of an IUS?
• Are there any risks?
• Can anyone use an IUS?
• I've just had a baby. Can I use an IUS?
• Can I use an IUS after a miscarriage or abortion?
• Where can I get an IUS?
• How is an IUS put in?
• What if I feel unwell after the IUS is put in?
• How will I know that the IUS is still in place?
• Is it safe to use tampons if I have an IUS fitted?
• When can the IUS be removed?
• Will an IUS affect my periods?
• What if I become pregnant while I am using an IUS?
• How often do I need to see a doctor or nurse?

What is the difference between an IUS and an IUD?

An intrauterine system (IUS) is a small plastic device that is inserted into the uterus and slowly releases a hormone called progestogen. An intrauterine device (IUD) is a small plastic and copper device that does not contain any hormone.

How effective is an IUS?

How effective any contraceptive method is depends on how old you are, how often you have sex and whether you follow the instructions.

If 100 sexually active women don’t use contraception, 80–90 will become pregnant in a year.

The IUS is over 99 per cent effective. Less than one woman in every 100 women who use the IUS will get pregnant over five years. The IUS is a method of long-acting reversible contraception (LARC). All LARC is very effective because while it is being used you do not have to remember to take or use contraception.

When will an IUS start to work?

The IUS can be fitted any time in your menstrual cycle if it is certain that you are not pregnant. If it is fitted in the first seven days of your menstrual cycle you will be immediately protected against pregnancy. If it is fitted at any other time, you will need to use an additional contraception or the first seven days. If you have a short menstrual cycle with your period coming every 23 days or less, starting the IUS as late as the seventh day of your cycle may not provide you with immediate contraceptive protection. This is because you may release an egg (ovulate) early in your menstrual cycle. You may wish to talk to your doctor or nurse about this and whether you need to use additional contraception for the first seven days.

How does an IUS work?

• It makes the lining of your uterus thinner so it is less likely to accept a fertilised egg.
• It also thickens the mucus in your cervix. This makes it difficult for sperm to move through it and reach an egg.
• In some women it stops the ovaries releasing an egg (ovulation), but most women who use an IUS continue to ovulate.

What are the advantages of an IUS?

• It works for five years.
• Your periods usually become much lighter and shorter, and sometimes less painful. They may stop completely after the first year of use. An IUS can be useful if you have heavy, painful periods.
• Can be used if you are breastfeeding.
• Your fertility will return to normal when the IUS is removed.
• It is useful if you cannot use estrogens, like those found in the combined pill, the contraceptive patch and the contraceptive vaginal ring.
• The IUS is not affected by other medicines.

What are the disadvantages of an IUS?

• Your periods may change in a way that is not acceptable to you (see Will an IUS affect my periods?).
• Some women report having acne, headaches and breast tenderness.
• Some women develop small fluid-filled cysts on their ovaries. These are not dangerous and do not usually need to be treated. Often there are no symptoms, but some women may have pelvic pain. These cysts usually disappear without treatment.
• An IUS does not protect you against sexually transmitted infections, so you may need to use condoms as well. If you get an infection when the IUS is in place this could lead to pelvic infection if it is not treated.

Are there any risks?

• There is a very small chance of you getting an infection during the first 20 days after an IUS is put in. You may be advised to have a check for any existing infection before an IUS is fitted.
• The IUS can be pushed out by your uterus (expulsion) or it can move (displacement).This is not common and is more likely to happen soon after it has been put in and you may not know it has happened. This is why your doctor or nurse will show you how to check your IUS threads every month.
• It is not common, but there is a risk that an IUS might go through (perforate) your uterus or cervix when it is put in. This may cause pain, but often there are no symptoms. If this happens, the IUS may have to be removed by surgery. The risk of perforation is low when an IUS is fitted by an experienced doctor or nurse.
• If you do become pregnant while you are using the IUS there is a small risk of ectopic pregnancy. The risk of ectopic pregnancy is less in women using an IUS than in women using no contraception.

Can anyone use an IUS?

Most women can use an IUS including women who have never been pregnant and women who are HIV positive. Your doctor or nurse will ask you about your own and your family’s medical history. Do mention any illness or operations you have had as some may require specialist care when the IUS is fitted. Some of the conditions which may mean you should not use an IUS are:

• you think you might already be pregnant.

You have now or had in the past:

• breast cancer or breast cancer within the last five years
• cirrhosis of the liver and liver tumours
• unexplained bleeding from your vagina (for example between periods or after sex)
• arterial disease or history of serious heart disease or stroke
• an untreated sexually transmitted infection or pelvic infection
• problems with your uterus or cervix.

I've just had a baby. Can I use an IUS?

An IUS is usually put in from four weeks after a vaginal or caesarean birth. You will need to use another method of contraception from three weeks (day 21) after the birth until the IUS is put in. It can also be put in within 48 hours of birth.

An IUS can be used safely while you are breastfeeding and will not affect your milk supply.

Can I use an IUS after a miscarriage or abortion?

An IUS can be put in by an experienced nurse or doctor immediately after a miscarriage or abortion. You will be protected from pregnancy immediately.

Where can I get an IUS?

You can go to a contraception or sexual health clinic. Some doctors and nurses at your general practice will also fit an IUS.

How is an IUS put in?

The IUS is fitted inside the uterus by a trained doctor or nurse. They will examine you internally to find the position and size of your uterus before they put in an IUS. Sometimes they will check for any possible existing infection. It is best to do this before the IUS is put in. Sometimes you may be given antibiotics at the same time as the IUS is fitted.

Fitting an IUS takes about 15–20 minutes. It can be uncomfortable or painful for some women, and you might want to use a local anaesthetic. Your doctor or nurse should talk to you about this beforehand. You may get period-type pain after the IUS is fitted. Pain relieving drugs can help with this.

What if I feel unwell after the IUS is put in?

If you feel unwell and have any pain in your lower abdomen, with a high temperature or a smelly discharge from your vagina, see a doctor or go back to the clinic where it was fitted as soon as possible. You may have an infection.

How will I know that the IUS is still in place?

An IUS has two threads attached to the end that hang a little way down through your cervix into the top of your vagina. The doctor or nurse will teach you to feel for the threads to make sure the IUS is still in place. You should do this a few times in the first month and then after each period or at regular intervals.

It is very unlikely that an IUS will come out, but if you cannot feel the threads or if you think you can feel the IUS itself, you may not be protected against pregnancy. Use additional contraception, such as condoms and see your doctor or nurse straightaway. If you had sex recently you might need to use emergency contraception.

Rarely, a partner may say they can feel the threads during sex. If this is the case, get your doctor or nurse to check the threads.

Is it safe to use tampons if I have an IUS fitted?

Yes, you can use tampons or towels.

When can the IUS be removed?

A trained doctor or nurse can take out the IUS at any time, by pulling gently on the threads. If you are not going to have another IUS put in, and you don’t want to become pregnant, use additional contraception, such as condoms, for seven days before the IUS is taken out. This is to stop sperm getting into your body. Sperm can live for up to seven days inside your body, and could fertilise an egg once the IUS is removed. Your fertility returns to normal after the IUS is taken out.

If you want to try for a baby start pre-pregnancy care such as taking folic acid and stopping smoking. You can ask your doctor or nurse for advice.

Will an IUS affect my periods?

Yes. In the first six months it is common to have irregular bleeding or spotting. Periods may become lighter than usual or may continue to be irregular and many women find that their periods stop altogether. If this happens to you, do not worry, it is perfectly healthy.

What if I become pregnant while I am using an IUS?

Very few women become pregnant while using an IUS. If you do become pregnant there is a small increased risk of you having an ectopic pregnancy. An ectopic pregnancy develops outside your uterus, usually in a fallopian tube. If you think you might be pregnant and/or have a sudden or unusual pain in your lower abdomen, seek medical advice as soon as possible. This might be the warning sign of an ectopic pregnancy.

If you are pregnant, the IUS should be removed as soon as possible, whether or not you wish to continue with the pregnancy. if you want to continue the pregnancy, removing the IUS can increase the risk of miscarriage.

How often do I need to see a doctor or nurse?

You need to have your IUS checked by a doctor or nurse 3–6 weeks after it is put in. The IUS can stay in for five years, or longer if you are over 45 years old. If you have any problems, questions or want the IUS removed you can go and see your doctor or nurse at any time.

Last updated November 2012. Next update available October 2013.