It works mainly by stopping the egg and sperm from meeting. It may also prevent the fertilised egg from attaching to the lining of the uterus. The copper also has a spermicidal effect (kills sperm).
Modern IUD’s are 99% effective or more. This means that up to 1 woman in 100 will become pregnant each year using this method of contraception. (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). There are different types of IUD. Older ones were slightly less reliable – about 98% effective.
Once an IUD is inserted you can forget about contraception. So, unlike the pill, you don’t need to think about contraception every day. It does not interfere with sex. It is not a hormonal method so it has no side effects on the rest of the body. Most women can have an IUD if they wish.
Most women with an IUD have no problems, but the following occasionally occur.
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 IUD 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.
Fitting an IUD can sometimes be uncomfortable. Once the IUD has been inserted some women have cramping pains like period pains for a few hours afterwards. These can be eased by painkillers such as paracetamol. Light vaginal bleeding may also occur for a short while.
The IUS is a small device made from plastic and contains progestogen hormone. Therefore, it is called an intrauterine system (IUS) and not just an intrauterine device (IUD). Mirena is the only IUS available in the UK, although others will probably become available. The IUS is put into a woman’s uterus (womb) by a doctor or nurse. It works for five years before needing replacing.
It works differently to an IUD as 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).
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.)
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.
Most women have no problems, but the following occasionally occur.
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: headaches, mood swings, weight gain, reduced sex drive, fluid retention, increase in acne, and breast discomfort.
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. However, the number of women this affects is small.
The IUS has become popular as a treatment for heavy periods (menorrhagia). In most treated women, bleeding becomes very light, or stops altogether, within 3-9 months. In one study, the IUS was inserted into women on a waiting list for hysterectomy for heavy periods. 8 in 10 of these women then decided against having a hysterectomy as the IUS worked so well. It has been mainly studied in women who have heavy periods due to ‘Dysfunctional Uterine Bleeding’. This is the commonest cause of heavy periods. It may not be suitable for heavy periods due to other causes such as fibroids.
It is usually fitted within seven days after the start of a period. It is then immediately effective. If it is fitted after the 7th day then you need to use other forms of contraception such as condoms for seven days.
You will need a vaginal examination, and the doctor or nurse will pass a small instrument into the uterus to check its size and position. An IUS is then fitted. You will be taught how to feel the threads of the device 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.