The Mirena Intrauterine Sytem

The Mirena IUS is a small T-shaped plastic device, which contains the hormone levonorgestrel, a type of progestogen. This is similar to the natural progesterone that women produce in their ovaries. The IUS slowly releases the progestogen hormone and works for up to five years.

How Effective is an IUS?

The IUS is over 99% effective. This means of every 100 women who use an IUS, less than 1 woman will get pregnant in a year. It starts to work immediately, if it is fitted within the first 7 days of your menstrual cycle. If it is fitted at any other time, you will need to use an extra contraceptive method for the first 7 days.

How Does an IUS Work?

It makes the lining of your womb thinner so it is less likely to accept a fertilised egg. It also thickens the mucus from your cervix, which 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 do ovulate

What are the Advantages of an IUS

• It works for 5 years
• You don't have to think about contraception for as long as it works
• It doesn't interrupt sex
• Your periods usually become much lighter and shorter, and sometimes less painful, so an IUS is also useful if you have heavy periods or painful periods
• Fertility returns quickly when the IUS is removed
• Unlike some methods of contraception, the IUS is not affected by other medicines

What are the disadvantages of an IUS?

• Most women have irregular bleeding for the first 3 months
• You may get temporary side-effects such as headaches, spotty skin and breast tenderness
• An IUS does not protect you against sexually transmitted infections, so you may need to use condoms as well
• The IUS can rarely be pushed out of the womb (expulsion) during a period. You will need to check your IUS threads every month
• There is a tiny risk that an IUS might go through (perforate) your womb

Can Anyone Use the IUS?

Most women who want to use an IUS can do so, including women who have never been pregnant.

An IUS can be fitted at any time of your menstrual cycle. Fitting an IUS takes about 15-20 minutes. It can be slightly uncomfortable. You may experience crampy period-like pain. Your specialist can remove the IUD in a few seconds at any time if there are problems.