Mirena coil (IUS)




The Mirena Intra-Uterine System (IUS)


What is it?

Mirena is a hormone releasing intrauterine system (IUS), often called a coil, which is placed in the uterus to prevent pregnancy for up to five years.

It is a T-shaped piece of flexible plastic about the size of a two-pound coin. It contains the progestrogen hormone levonorgestrel, which is also found in many birth control pills. The hormone is released directly into the uterus which means only small amounts enter the bloodstream (equivalent to three ‘mini-pills’ a week).

Two threads are attached to the stem of Mirena and these are the only parts you can feel once the Mirena is in the right position. If they are too long and causing any bother after fitting they can be trimmed to a shorter length if wished.

The Mirena lasts up to five years for birth control but can be removed at any time. You can assume immediate return to your normal fertility level once it is removed. If you have Mirena fitted for contraception at the age of 45 or over it can remain in place (and will still be effective) until the end of menopause or age 55, whichever comes soonest.

Mirena can also be used to provide the progestogen part of combined HRT but must be changed after five years if it is being used for this.


How does it work?

It is not known exactly how Mirena works. It probably has a combination of effects: thickening cervical mucus (causing a barrier to sperm), thinning the lining of the uterus and inhibiting sperm movement. For some women it also prevents ovulation although this is not the way it works in most cases. All of these changes are reversed when the device is removed.

If the Mirena is fitted in the first seven days of your cycle (counting the first day of your period as day 1) you will not need to use any additional precautions. At any other time you must use additional contraception for seven days before you are protected from pregnancy.


Are you able to have a Mirena IUS?

We cannot fit Mirena if any of the following apply:

  • You are pregnant
  • You have a past history of the serious pelvic infection called Pelvic Inflammatory Disease (PID) - unless you have had a normal pregnancy since the infection
  • You have an untreated pelvic infection now
  • You have cancer of the uterus, cervix or breast
  • You have unexplained bleeding from the vagina
  • You have liver disease or a liver tumour
  • You have a known condition that has changed the shape of the uterine cavity, such as large fibroids

Are you aware of the potential risks and complications?

As with any medical device, there are risks associated with the use of Mirena. These are outlined below:

  • Ectopic pregnancy: Very few pregnancies overall occur with Mirena in place. This means that the OVERALL risk of ectopic pregnancy is reduced compared to using no contraception. However if a pregnancy does occur with Mirena in situ up to half of those pregnancies will be ectopic. This is why it is very important to alert the doctor immediately if you think you may be pregnant.
  • Pregnancy: Mirena is an extremely effective method of contraception. If pregnancy does occur with Mirena in place, Mirena should be removed; and this removal or manipulation may cause pregnancy loss. It can cause complications if it remains in place throughout a pregnancy, for example by increasing the risk of septic miscarriage (miscarriage where the mother becomes ill from infection).
  • Pelvic Inflammatory Disease: There is a risk of introducing any pre-existing or new infection into the uterus when Mirena is inserted, or if you have a Mirena in place. PID can cause tubal damage leading to ectopic pregnancy or infertility or hysterectomy.
  • Perforation: May occur during insertion and not be detected until some time later. Risk is about 1-2 per 1000 insertions. Perforation may allow a pregnancy to occur. You may require surgery to remove the Mirena. Delayed detection may result in migration outside the uterine cavity, with a risk of adhesions, internal infection, and/or perforation of intestine.
  • Expulsion: May occur without you noticing. The risk is around 1 in 20 and is most common in the first year of use, particularly within the first three months after insertion.
  • Ovarian Cysts: Mirena is associated with an increase in ovarian cysts. These are benign and usually completely asymptomatic and ordinarily disappear spontaneously.
  • Irregular bleeding: For the first 3-6 months bleeding and spotting days may be increased and bleeding patterns may be irregular. You may bleed most days in the early weeks after insertion but in most women this will eventually either stop or become much lighter. May women have no periods at all on Mirena.

Do you need a swab before fitting?

The Faculty of Sexual and Reproductive Health states that any woman with the following risk factors must have a swab to check for sexually-transmitted infection prior to fitting a Mirena or copper coil:

  • Being sexually active and aged under 25
  • Having a new sexual partner in the last three months
  • Having more than one sexual partner in the last year
  • Having a regular sexual partner who has other sexual partners
  • A history of sexually-transmitted infections

If any of these apply to you, please request a self-test swab for chlamydia and gonorrhea from Bridge Street reception a week before your fitting is scheduled. Ask reception for a QUICK CHECK TEST. This is a simple vaginal swab, the instructions are in the packet. Drop it back to reception when you are done. (You are very welcome to pick up this test anyway if you would like, even if you don’t fit into any of the suggested categories).



Unfortunately we do have a waiting list for coil and implant clinics at Bridge Street - this is common nationwide as there is a shortage of fitters. After you have had a phone appointment with any clinician to assess your suitability for a coil and answer any questions, we can add you to the waiting list and reception will contact you as soon as the next appointment comes up.

We can fit Mirena at any time in your cycle, including during menstruation as long as your bleeding is not too heavy. However it is vital you are not pregnant at the time of fitting.


Contraceptive precautions before your appointment

  • If you are not using any contraception or are only using condoms: Do not have sex (even using condoms) from when your period starts until the fitting.
  • If you take the contraceptive pill or have a contraceptive implant or injection: Make sure you continue to use your current method of contraception.
  • If you are having the coil removed or replaced: Do not have sex for 10 days before the fitting. This is to ensure there are no live sperm in your uterus, in case the new coil cannot be fitted once the old one has been removed.


Please ensure you have eaten prior to your appointment (ie, do not skip breakfast). We would recommend taking an anti-inflammatory painkiller, such as ibuprofen, about an hour before your appointment (as long as you are able to take this medication usually). You can also take paracetamol as well as, or instead of, ibuprofen.

There will be a GP and an assistant present at your appointment. We will first review what we’re going to do and go through the consent form.

The GP will do a pelvic examination to assess the size and shape of your uterus. The rest of the procedure is carried out using a speculum (the device that is used during a smear test). The fitting can cause some discomfort – the sensation has been described as like a sharp pinch, or a strong period cramp. We use anaesthetic gel to try and make things easier, and we work hard to try and make the clinic as painless as possible. If at any point you wish to stop the procedure we will of course stop immediately.

Fitting usually takes half an hour or less. Very rarely, some women can experience a vasovagal reaction during or after fitting and can faint. If this occurs we will ask you to stay on the premises until we are sure you are feeling well enough to go home.


Follow up

You are not obliged to have any formal follow-up although we do ask that you are aware of your threads and check them regularly. If you do wish for follow up you are most welcome to book an appointment with the nurse at 3-6 weeks after insertion for a thread check (this is carried out by performing an examination with a speculum – it is quick!). If you don’t want a vaginal examination please feel free to request a nurse phone call instead to go through any questions or concerns.


If any of the following occurs please contact the GP urgently:

  • pain or discomfort after 48 hours have passed since fitting
  • severe pain or concerning bleeding at any time
  • an unusual or odorous vaginal discharge or fever
  • if you cannot feel your threads or if you think the Mirena has been expelled for any reason (use contraception until you can see the doctor or nurse in case the device has been expelled or perforated)
  • if you have a positive pregnancy test
  • if you develop new migraine or exceptionally severe headache; jaundice; increase in blood pressure; stroke or heart attack

After a few months with Mirena many womens’ periods will stop. Please carry out a pregnancy test if you have not had a period for six weeks or longer. If this is negative you need not keep testing but can assume you are likely to remain free of periods while the Mirena is in place (this is not harmful to your fertility in any way and your periods will resume whenever the Mirena is removed).



You can have Mirena removed at any time. Taking it out is usually quick and easy (five minutes or less) and can be performed by the nurse. Occasionally we are unable to remove Mirena at the surgery, in which case we will refer you to the gynaecology department at Addenbrookes. Please be aware you need to have abstained from sex for a week prior to removal as otherwise there is a risk of pregnancy.

Find out more about other contraceptive options on our Sexual Health page here