What is a Mirena?

Mirena is a hormonal intrauterine device (IUD) that is inserted into the uterus for long-term contraception. It is a plastic frame that releases a hormone called progesterone. It works by thickening the cervical mucus to prevent sperm from reaching or fertilizing an egg. Mirena also thins the lining of the uterus and partially suppresses ovulation.

The advantages of a Mirena

  • The hormone in Mirena will last for five years
  • It is a reliable contraceptive lasting 5 years with a very low failure rate similar to sterilisation rates and does not depend on the user remembering to do anything
  • It can be removed at any time, followed by a return to baseline fertility
  • It decreases menstrual bleeding within three to six months
  • It decreases severe menstrual pain and pain related to endometriosis
  • It decreases the risk of endometrial cancer
  • It can be used while breast-feeding
  • It can be used as the progesterone component of HRT


Some disadvantages of Mirena

  • It does not regulate an irregular cycle so bleeding can be unpredictable although is usually light
  • It does not prevent sexually transmitted diseases, but also does not increase the risk of them affecting fertility
  • It does not have some of the benefits seen with oestrogen (in the contraceptive pill)

Some women may be better not to use Mirena

  • Women who have had some types of breast, uterine or cervical cancer
  • Women who have certain types of fibroids
  • Women who have expelled an IUCD in the past

Some women believe they are not suited to using a Mirena if they have not had children. There is no reason to avoid a Mirena in this situation, but sometimes inserting it can be a little more difficult, however even so most women can still have one fitted in the rooms using some local anaesthetic.

What happens before a Mirena is inserted?

Prior to insertion of a Mirena any existing problems need to be investigated. Therefore it is important to be up to date with your Pap smear, to have screening with swabs for infection if you are at risk and to be certain you are not pregnant.

Insertion is usually done in the rooms using local anaesthetic. Some women require a general anaesthetic. Taking paracetamol and a nonsteroidal anti-inflammatory drug, such as ibuprofen (Nurofen) one to two hours before the procedure can help reduce cramping.

What are the risks of insertion?

Some discomfort is common with insertion however this will resolve quickly for most women. Infection can be introduced into the uterus however screening for infection prior to insertion reduces this risk. There is a small risk of failure to be able to insert the device and a small risk of injury to the wall of the uterus when the device is inserted.

After the procedure

You should avoid intercourse for 7 days after a Mirena is inserted

Mirena is a great contraceptive method with less than 1% of women falling pregnant, but it does not prevent pregnancy which was conceived in the week before it was inserted. A small number of women will expel the Mirena device and this most commonly occurs with heavy bleeding however it is possible not to see the device pass out of the vagina, so it is important to check for the strings at the top of the vagina after any heavy bleeding or if there is a change in your pattern of bleeding after the initial 3 month settling in stage.

What to expect

I advise women to expect unpredictable spotting in the initial stages and the first few periods may not be much different but most women have very light or no periods by 6 months.

Any of the following symptoms in the first few weeks after insertion would be considered to be abnormal and require urgent medical assessment:

  • Smelly vaginal discharge
  • Heavy bleeding
  • Severe pain
  • Fever and abdominal pain
  • Being unable to feel the threads at the top of the vagina. (In this situation often the device is still in the uterus and this is not a medical emergency if there are no other abnormal symptoms, however another form of contraception should be used until an ultrasound confirms the device is still in the uterus.