Intrauterine System

What is the IUS?

The IUS is a small device that is put into a woman's uterus (womb) by a doctor or nurse. It is made from plastic and contains progestogen hormone. Therefore, it is called an intrauterine system (IUS) and not just an intrauterine device (IUD). An IUS works for five years before it needs replacing.

Mirena® is the only IUS available in the UK, although others will probably become available in the future.

How does the IUS work as a contraceptive?

It works differently to an IUD because an IUS includes a progestogen hormone. It works mainly by thickening the mucus made by the cervix which forms a 'mucus plug' in the cervix. This stops sperm getting through to the uterus (womb) to fertilise an egg. The progestogen also makes the lining of the uterus thinner. This makes it unlikely that a fertilised egg will be able to attach to the uterus. It may also have some effect on the ovary, and ovulation may not occur (the release of the egg each month).

How effective is the IUS for contraception?

It is more than 99% effective. This means that less than 1 women in 100 who use the IUS will become pregnant each year. (Compare this to when no contraception is used. More than 80 in 100 sexually active women who do not use contraception become pregnant within one year.)

What are the advantages of the IUS?

Once it is inserted you can forget about contraception for five years. It does not interfere with sex. Periods usually get lighter, less painful and often stop (unlike the IUD). After 12 months most users only have a light bleed for one day per month, and about 1 in 5 users have no bleeding at all. Fertility returns as soon as it is removed.

The IUS is often used as a treatment for heavy periods, even in women who do not actually need contraception. It is also used as a treatment for endometriosis and fibroids.

What are the disadvantages of the IUS?

Although the majority of women with an IUS have no problems, the following may occasionally occur:

Irregular bleeding. This may occur for the first three to six months, but usually settles down. It is usually a light "spotting" of blood which some women can find a nuisance.

Expulsion. Rarely the IUS may come out without you noticing.

Damage to the womb. The fitting of an IUS can very rarely cause damage to the uterus (womb

Are there any side-effects?

Side-effects are uncommon. The progestogen released by the IUS mainly stays around the uterus and very little gets into the bloodstream. Therefore, side-effects are less common than with other progestogen forms of contraception such as the progestogen only pill and the contraceptive injection or implant. If side-effects do occur, they tend to develop just in the first 3-6 months, and then tend to ease and go. Examples of possible side-effects include: mood swings, reduced sex drive, fluid retention, increase in acne and breast discomfort.

There is no evidence that women with an IUS in put on weight.

Who cannot use the IUS?

Your doctor or family planning nurse will discuss any current and past illnesses. Some illnesses may mean you cannot use progestogen-based contraceptives such as the IUS. These include recent breast cancer, very large fibroids or an infection which has not been treated. However, the number of women who cannot have the IUS inserted is small.

How is the IUS fitted?

This is usually done towards the end of a period or shortly after. However, it can be fitted at any time provided that you are certain you are not pregnant. You will need to have a vaginal examination. The doctor or nurse will pass a small instrument into your uterus to check its size and position. An IUS is then fitted. You will be taught how to feel the threads of the IUD so you can check it is in place. It is best to check the threads regularly, for example, once a month just after a period.

If it is fitted within seven days after the start of a period then it is immediately effective as a contraceptive. If it is fitted after the 7th day then you need to use other forms of contraception such as condoms for seven days.

Follow up

The doctor or nurse will usually want to check that there are no problems a few weeks after fitting. After this, there is no need for any routine check until it is time to remove the IUS. However, see your doctor or nurse at any time if you have any problems or queries.

Most women have no problems and the IUS can remain in place for five years. It needs to be replaced after five years if you wish to continue using this method of contraception. It can be removed at any time by a trained doctor or nurse.

Fertility returns as soon as it is removed. If you plan to have it removed, but do not want to get pregnant, then use other methods of contraception (such as condoms) from seven days before it is removed. This is because sperm can last up to seven days after having sex.

You can use sanitary towels or tampons for periods when an IUS is in place.

You should consult a doctor if any of the following occur:

• Prolonged abdominal pain after an IUS is inserted.
• Vaginal discharge with or without pain (which may indicate infection).
• If you suspect that the IUS has come out or is coming out. It is usually possible to feel the threads of the IUS inside the vagina to check it is in place. If you cannot feel the threads then use other contraceptive methods (such as condoms) until you have been checked by a doctor or nurse.

Further information

Your GP and practice nurse are good sources of information if you have any queries.

The fpa (formerly the family planning association) also provide information and advice.
fpa's Helpline: 0845 310 1334 or visit their website www.fpa.org.uk