The Coil - IUD and IUS

July 2017

The coil is a small T-shaped plastic device which is fitted by trained professionals into your womb.

One of the most commonly used contraception in the world, except in the UK where it is used less than the oral contraceptive pill.

There are 2 types of coil used in the UK:
1. The IUD or copper coil
2. The IUS or Mirena coil

How effective is the coil?

Both the IUD and IUS are over 99% effective if used correctly - this means that on 100 women following the methods for one year, only one of them would get pregnant.

How does it work?

The IUD destroys sperm and hence stops them from reaching your egg.
The IUS releases progesterone and therefore works in 2 ways:
  • It causes thickening of your cervical mucus so that sperm cannot get through ;
  • It causes the lining of your womb to be thiner, so that there is less chance that a pregnancy could implant and progress.

The coils are both termed long-acting reversible contraception:
  • IUD can be used for 5 - 10 years
  • The IUS is used for 5 years

A trained doctor in your local GP surgery or family planning clinic will be able to fit the coil - it usually takes approximately 20 minutes. The coil is effective immediately if inserted at the beginning of your period, otherwise it will take 7 days. All coils have threads that hang through your cervix which allows you and your doctor to check the coil is in the correct position


You do not have to remember to take a pill each day. The coil does not interrupt sex unlike condoms. If you have the IUS, your monthly period should become lighter and less painful. Some women do not have periods at all.

You can have the coil fitted 4 weeks after giving birth, even if you are breastfeeding. The IUD is useful if you cannot take hormonal contraception. The coils last for at least 5 years.

If you have the coil fitted after the age of 40 years (IUD) or 45 years (IUS), it can be left in until after you are menopausal

Disadvantages and Risks

Some contraindications to having the coil include pregnancy, vaginal infections, abnormal womb anatomy, liver disease, breast or gynaecological cancer, unexplained vaginal bleeding, or cardiovascular disease (e.g. heart attacks/strokes). The IUD can make your periods heavier and longer. Irregular bleeding with the IUS - you can experience spotting and erratic vaginal bleeding. This tends to settle with time but for some women, becomes unacceptable and requires removal

With the IUS, you might experience side-effects of the progesterone itself - such as bloating, weight gain, headaches, breast tenderness or mood changes

During insertion, there are small risks include the coil making a hole in your womb (perforation), moving, or falling out (expulsion).

There is a small risk of womb infection in the first 3 weeks after insertion - your GP may arrange for you to have vaginal swabs before inserting the coil to reduce this risk

It may be difficult to remove the coil, especially if it has moved location and the threads cannot be seen

There is no protection against sexually transmitted infections (STIs)

Your partner may feel the strings from your coil - this means that they you should return to your surgery or family planning clinic for the threads to be shortened

Further sources on information

You can find information on the Family Planning Association website:


Stérilet - DIU - Dispositif intra-utérin
Stérilet - DIU - Dispositif intra-utérin
Dispositivos intrauterinos, DIU
Dispositivos intrauterinos, DIU
Latest update on May 30, 2014 at 07:41 AM by Ambucias.
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