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Mirena or IUS (The Intrauterine System)

What is the Mirena?
The Mirena or IUS is a small plastic T-shape device containing the hormone Progestogen, and is fitted into the womb. It releases the hormone slowly over a period of five years. The IUS was first developed as a contraception, but it is also very effective at reducing heavy periods and helps many women avoid hysterectomy. It can also be used in Hormone Replacement Therapy (HRT) to provide the progesterone needed to protect the lining of the womb (endometrium). The IUS lasts for five years after which it must be removed and replaced with a new device.

How does the IUS work?
• The hormone in the IUS makes the lining of the womb very thin and so very little to come away at period time

The IUS as a Contraceptive
• The failure rate is 1 in 500 women yearly compared to female sterilisation, which is 1-3 per 1000 women
• Because it thickens the cervical mucous, it is difficult for the sperm to get through to reach the egg
• It makes the lining of the womb very thin and therefore unsuitable for a pregnancy to occur

How effective is the IUS at reducing menstrual blood loss?
• Long term most women will notice a marked reduction in their menstrual loss, and some women find their periods stop altogether
• After 5 years over 90% of women have no periods or will have only occasional bleeding
• Period pain is often reduced and in some women the IUS may help reduce symptoms of PMS
• 2 out of 3 women will avoid a hysterectomy
• The IUS may also shrink Fibroids
• Periods will return to their previous pattern if the IUS is removed unless you have become menopausal

IUS and HRT?
• Oestrogen, the hormone in HRT is used to make the lining of the womb thicker. A progesterone is needed to prevent this happening and the IUS does this very effectively. After one year bleeding is uncommon, and the oestrogen can be taken by route of choice

Are there any disadvantages?
• Irregular bleeding, prolonged lighter periods, and spotting may occur during the first three months but this settles down by six months
• Some women may experience breast tenderness which will settle in time. Taking Evening Primrose Oil may help
• Slight weight gain, greasy skin or mood changes may occur. These side effects are common to all progestogens but less likely to occur with the IUS


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