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Mirena - An Introduction

The Mirena IUD is the most effective method of birth control . A Mirena (levonorgestrel - LNG IUS) is similar in shape and size to some intra-uterine contraceptive devices (Figure 14.1 ; IUCDs - Coils that have been used in family planning for many years. A Mirena slowly releases the hormone levonorgestrel locally within the uterine cavity.

Mirena IUS (Intrauterine System)

Mirena IUS - Intrauterine system

Although primarily a method of birth control, the Mirena has found a place in the management of heavy periods, PMS, HRT and endometriosis. The Mirena had been available for routine clinical use in Scandinavia for five years before it was licensed in the UK in May 1995.

How does the Mirena work?

Although the Mirena is physically similar to other IUCDs, its main mode of action is similar to progestogen-only pills. The mucus in the neck of the womb remains thick and hostile to sperm throughout the menstrual cycle; this thick mucus prevents sperm reaching the eggs and fertilisation is therefore unlikely to occur. Furthermore, the lining of the uterus is kept thin by the Mirena so that even if an egg should be fertilised, a pregnancy cannot be supported. For some, the question of how the IUCD prevents pregnancy is critical. As IUCDs are effective partly after fertilisation, they may not be acceptable in some cultures. The Mirena functions almost entirely to prevent fertilisation.

How is the Mirena introduced into the uterus?

Like other intrauterine devices, a Mirena is best introduced at the end of or just after a period. It has a slightly larger diameter (5mm) than most other devices so the neck of the womb may have to be stretched a little (dilated). This can usually be accomplished with a local anaesthetic injection. If there is an indication to perform a  - (heavy periods, for example), the Mirena can be introduced under the same anaesthetic.

Prostaglandins provide a medical means to open the cervix. Some gynaecologists prescribe Misoprostol 2 x 200 mg introduced deep into the vagina three hours before planned introduction may assist. Ibuprofen 400 mg one hour before insertion provides very effective pain relief and may be repeated a few hours later. Erythromax capsule (erythromycin 250mg) is sometimes used about an hour before insertion to reduce the chance of infection.

How quickly will a Mirena work?

Provided the Mirena is introduced at the correct time, it is effective immediately. It can be introduced at any time if you are currently taking the pill. Generally, we recommend waiting until the first check, which is usually scheduled about six weeks after fitting.

For How long will my Mirena work?

The Mirena is licensed for five years although there is some evidence that it may be effective for at least eight years.

How failsafe is the Mirena?

The Mirena is associated with only 0.2 pregnancies/100 woman years . This is less than combined pills, progesterone only pills, other IUDs, and even female sterilisation (0.4/100 women years).

What side effects can occur with the Mirena?

Spotting for the first two or three months after insertion is a relatively frequent side-effect.  As with other intrauterine devices, a Mirena could be expelled from the womb - it should be checked about six weeks after insertion. Very rarely, the device can go through the uterus (perforation).

There is no evidence that the Mirena increases body weight.

What will happen to my periods after a Mirena is introduced?

Blood loss diminishes quite markedly with a Mirena and this will be a bonus for you if your periods are heavy and painful. You may, however, experience a tendency for spotting through the first two or three months after introduction. A panty liner will usually suffice. The spotting will almost always settle down. Some women stop seeing their periods altogether although the cycle will return once the device is removed. From a medical point of view there is no anxiety if your periods are absent if you have a Mirena. It is a natural phenomenon before puberty, during pregnancy and breast-feeding and after the menopause. Periods are not required by the body to get rid of waste material.

How would a Mirena affect my fertility?

When the Mirena is removed from your uterus, fertility will be restored immediately.

What value is Mirena for premenstrual syndrome (PMS)?

Premenstrual syndrome is a common problem although for the majority of women the symptoms are only mild . Some women, however, have more major and sometimes debilitating difficulties. Oestrogens often given as a small implant introduced under the skin with local anaesthetic, can alleviate symptoms but if the uterus is present progestogens must also be given to prevent the lining of the womb becoming too thick. Until recently, the progestogens had to be administered as tablets taken cyclically for about 12 days each month (to produce a withdrawal bleed and this could reproduce PMS type problems). If a Mirena is introduced, there will be no cyclical thickening of the lining of the womb and no cyclical progestogen tablets are required.

What value is LNG-IUS with Hormone Replacement Therapy?

If the womb is present, oestrogen replacement therapy must be accompanied by progestogens. LNG-IUS can be used as the progestogen.

Could the Mirena have a place in the management of endometriosis?

Retrograde menstruation is a significant cause of endometriosis. From a theoretical point of view, as the Mirena is associated with reduced menstrual flow, the retrograde menstruation should be reduced, perhaps reducing the endometriosis. Further research is required in this exciting area.

Intrauterine progestogen (LNG-IUS) is effective in symptom control throughout the 3 years on the device, and discontinuation is greatest between 3 and 6 months. For those patients with improvement in symptoms, it is an acceptable long-term alternative.he is effective in symptom control throughout the 3 years on the device, and discontinuation is greatest between 3 and 6 months. For those patients with improvement in symptoms, it is an acceptable long-term alternative. The levonorgestrel intrauterine system is an effective hormonal option for treating symptomatic endometriosis (minimal to moderate). It also alters the American Fertility Society staging of disease. With a continuation rate of 68% after 6 months, it has the potential for providing long-term therapy in a substantial number of sufferers, although this would require further study and verification.


Could the Mirena have a place in the management of endometrial hyperplasia?

The Mirena has been shown to be effective in the management of endometrial hyperplasia.

The aim of this web site is to provide a general guide and it is not intended as a substitute for a consultation with an appropriate specialist in respect of individual care and treatment.

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