How Does the Mirena Coil Work?

Launched 33 years ago in Finland, the Mirena coil is nothing new. However, it was the first hormone-releasing intrauterine contraceptive device now used by approximately 160 million women worldwide.

This small plastic T-shaped device is used primarily as a highly effective method of contraception but also to help reduce heavy periods and to protect the lining of the womb during menopause.

How it works for contraception

The Mirena coil is designed to remain in place for 5 years before it is removed by your medical professional. A hormone called levonorgestrel is steadily released over the 5 year period. Levonorgestrel is a type of synthetic hormone which prevents ovulation and therefore pregnancy. In other cases, it works by thickening the cervical mucus therefore making it difficult for sperm to reach the egg. It also keeps the lining of the womb too thin to allow implantation of an egg.

If you need immediate or emergency contraception it is recommended that you have the Mirena coil inserted within 7 days from the start of your period. If more than 7 days has elapsed since the start of your period, it is recommended that you continue with another method of contraception until the start of your next period.

You can use the Mirena coil if you are still breastfeeding. Fertility will return to normal after you have it removed.

How it works for heavy periods

Because the Mirena coil thins the lining of the womb you will notice a reduction in bleeding every month. The coil prevents any abnormal thickening of the womb lining which can, in rare cases, lead to cancer. Some women have reported that their periods ceased altogether while using the coil. Period pains along with the usual symptoms of premenstrual syndrome can be reduced.

How it works as hormone replacement therapy (HRT)

The Mirena coil works by replacing the hormone progesterone which is the hormone your body stops producing during menopause.

If you have ongoing and regular menopause symptoms which are affecting your life your doctor may prescribe oestrogen to work alongside the coil to reduce your symptoms.

Are there any side effects?

Most medications have both advantages and disadvantages and the Mirena coil is no different. There are side effects which may or may not be experienced and these include:

• Erratic bleeding during the initial 3-6 months after insertion and this could include spotting or lighter periods which last longer than usual. Periods should stop altogether after this time.
• Breast tenderness can occur. This can be relieved by taking evening primrose oil.
• Weight gain.
• Acne.
• Mood changes.
• Headaches.
• Nausea.

Less common side effects include:

• Abdominal pain.
• Bloating or swelling of lower legs or ankles.
• Abnormal vaginal discharge.
• Heavy bleeding.
• Depression or anxiety.
• Ovarian cysts.

It is important to remember that not all of these side effects will be present and indeed many women experience no side effects at all.

You should talk to Mr Broome, Consultant Gynaecologist at Spire Manchester Hospital if you are at all worried about any aspect of having the Mirena coil fitted.

How is the Mirena coil fitted?

Following questions about your general health and any medications you are taking, the procedure will then be undertaken by a specialist who will use a vaginal speculum (the same instrument used in a smear test) to gain access. It should be painless although some cramp may be experienced during and after the procedure. This will soon settle down.

If any symptoms continue to occur or if there is any bleeding or offensive smelling discharge in the weeks following insertion of the coil you should make an appointment with your doctor. It can be removed quickly and easily by your doctor or gynaecologist.