The IUS is an effective method of contraception. It is also used to treat heavy periods (menorrhagia). Each device works for five years.
What is the IUS?
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.
How does the IUS work as a contraceptive?
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).
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.
What are the disadvantages of the IUS?
Most women have no problems, but the following occasionally occur.
- Irregular bleeding - may occur for the first three months or so, but usually settles down.
- Expulsion - rarely the device may come out without you noticing.
- Damage - the fitting of the device can (rarely) cause damage to the uterus. Also, there is possibly a very small risk of an infection of the uterus (pelvic infection) developing soon after the fitting of the device.
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: headaches, mood swings, weight gain, reduced sex drive, fluid retention, increase in acne, and breast discomfort.
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. However, the number of women this affects is small.
The IUS as a treatment for heavy periods (menorrhagia)
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.
How is the IUS fitted?
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.
