The Mirena IUD (intrauterine device), also known as the Mirena coil, is a hormonal device for controlled contraception. It is fitted under the uterus (the womb) and releases very low doses of a progesterone hormone called levonorgestrel.

Clinical uses of the Mirena IUD

The Mirena IUD is predominantly associated with contraception, but it may also be advised for women with the following conditions:

  • Endometriosis.
  • Chronic pelvic pain.
  • Heavy periods (menorrhagia).
  • Anaemia.
  • Dysmenorrhoea.

Fitting the Mirena IUD

The Mirena IUD must be put into place by a qualified and certified doctor, who will follow the manufacturer’s instructions using an aseptic technique to prevent bacterial infection. Women who have a high risk of endocarditis (an inflammatory condition that affects the heart) are normally given antibiotics before the IUD is fitted, to lower potential infection risks.

During the fitting procedure the cervix is widened or dilated, to enable doctors to determine the size of the uterus and then insert the device. Some women often find the dilation aspect of the procedure painful and it may be worthwhile to take pain-relief medication beforehand. There may be less discomfort if you have the device fitted mid-cycle, as this is the time when the cervix is dilated naturally.

Once the Mirena IUD has been fitted it will provide contraceptive protection for up to 5 years, and the 5 year rate of pregnancy for a Mirena IUD is approximately 0.7 percent.

Mechanisms of contraception

The Mirena IUD releases a daily 20 microgram dose of the hormone levonorgestrel. There is some debate around how the coil works exactly, but it is known to have a number of effects on the body in preventing pregnancy. These include:

  • Reducing the frequency of ovulation.
  • Changing the consistency of cervical mucus to reduce the possibility of sperm reaching the egg through the cervix.
  • Encouraging the release of prostaglandins and leukocytes from the endometrium (the lining of the womb), which creates a hostile environment for the eggs and sperm. This response is produced by the insertion of an unknown or foreign body into the uterus.
  • Thinning the endometrium to make it more difficult for eggs to implant.

Removing the Mirena IUD

The procedure to remove the Mirena IUD is usually more straightforward if carried out at the latter end of the natural cycle. The procedure involves using forceps to gently pull the IUD thread and remove the coil. If the thread cannot be found this is known as a ‘lost coil.’ If this is the case, forceps or thread-collecting devices may be used to locate the thread or to pull the IUD out of the cervix. In rare cases, when it is not possible to grasp the IUD, ultrasound scans may be carried out to locate the IUD. In very rare cases a hysteroscopy may be required, which involves using an endoscope to inspect the uterus.

Within a few months of the IUD being removed, fertility will return to normal and around 80 percent of women conceive within a year of having the Mirena IUD taken out.


Intrauterine devices or systems are sometimes unsuitable for certain women and the Mirena IUD should not be fitted in the following circumstances:

  • If a woman is pregnant.
  • If a woman has sepsis (an infection) after giving birth or having an abortion.
  • If a woman has an active sexually transmitted infection.
  • If a woman has PID (pelvic inflammatory disease) or has had a PID infection within the last 3 months.
  • If a woman has uterine abnormalities.
  • If a woman has cervical, ovarian or endometrial cancer and is waiting for treatment.
  • If a woman has pelvic tuberculosis.
  • If a woman has malignant trophoblast disease.

Complications and side-effects of the Mirena IUD

Location of the IUD

Once the IUD has been inserted into the uterus it is possible for the device to be rejected and expelled from the cervix. According to the trial research carried out by the manufacturer the expulsion rate is approximately 4 percent, with 3 percent occurring within the first 12 months of the coil being fitted. Rates of expulsion are higher with women who haven’t had children, women within a younger age bracket, and if an IUD is fitted shortly after giving birth or having an abortion.

Uterine perforation is a rare complication but it can be potentially serious. It may occur during insertion or after the coil has become embedded in the wall of the uterus (myometrium) and migrated into the abdominal cavity. Perforation can contribute to internal scarring, damage to surrounding organs and infection, and surgery may be required to repair any damage. The rates of perforation are estimated to vary between 1 and 2.6 per 1000 insertions; however, the actual figure may be higher as many perforations go unreported.

Perforation and expulsion inhibit the contraceptive qualities of the IUD, and it is important for women to check the location of the IUD thread on a regular basis to ensure its right location. Most doctors recommend self-checking once per cycle.

In some cases the string can be felt by males during sexual intercourse. If this is a problem the thread can be shortened, tucked behind the cervix or cut in line with the cervix. It is worth noting that cutting the threads will make it more difficult to check the location of the IUD and make removal of the IUD more complex.

Sexually transmitted infections (STIs) and Pelvic inflammatory disease

Pelvic inflammatory disease (PID) is often the result of a sexually transmitted infection. PID can cause infertility and is considered a serious condition. Having an IUD fitted will raise the risk of a woman getting PID if she has an STI. This is why it is not advisable for women with an STI or those with a high risk of developing them to have an IUD fitted.  

A study carried out using animals suggested that the risk of contracting HIV was slightly higher when using progestin-only hormonal contraceptives, because the walls of the vagina become thinner. However, studies carried out with humans have not found an elevated risk.

The IUD does not offer any protection against STIs. Only barrier types of contraception, such as a condom, can protect against both infections and unwanted pregnancies.

Post-abortion and post-partum insertion

An IUD can be fitted within 48 hours of post-partum (giving birth). After this period of time the risk of perforation is higher, as uterine involution is incomplete. Involution usually takes around 4-6 weeks after giving birth. Doctors will make special considerations for women who are breastfeeding.

IUDs are not advisable for those who have undergone a second trimester abortion within the last four weeks. If this is the case the woman will be advised to wait in order to enable complete uterine involution. IUDs are also unadvised for women who have undergone a medical abortion and have not had an ultrasound to make sure that the procedure was successful. Rates of expulsion are higher when IUDs are fitted shortly after abortion and childbirth.

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