Coils are devices inserted into the uterus that provide contraception. They are a form of long-acting reversible contraception. Once fitted, they work for a long time. Removing the device restores fertility.

There are two types of intrauterine device (IUD):

  • Copper coil (Cu-IUD): contains copper and creates a hostile environment for pregnancy
  • Levonorgestrel intrauterine system (LNG-IUS): contains progestogen that is slowly released into the uterus


Both types of coil are more than 99% effective when properly inserted. Fertility returns immediately after removal of an intrauterine device.

TOM TIP: Often, the two types of coils are referred to as IUD and IUS. The intrauterine device (IUD) refers to the copper coil, and the intrauterine system (IUS) refers to the levonorgestrel (e.g. Mirena) coil. The copper coil is just a “device”, whereas the hormones in the Mirena make it a “system”.



  • Pelvic inflammatory disease or infection
  • Immunosuppression
  • Pregnancy
  • Unexplained bleeding
  • Pelvic cancer
  • Uterine cavity distortion (e.g. by fibroids)



In women at increased risk of sexually transmitted infections (e.g. under 25 years old), screening for chlamydia and gonorrhoea is performed before insertion of a coil.

Specific qualifications are required to insert the implant. A bimanual is performed before the procedure to check the position and size of the uterus. A speculum is inserted, and specialised equipment is used to fit the device. Forceps can be used to stabilise the cervix while the device is inserted. Blood pressure and heart rate are recorded before and after insertion.

There may be some temporary crampy period type pain after insertion. NSAIDs may be used to help with discomfort after the procedure. Women need to be seen 3 to 6 weeks after insertion to check the threads. They should be taught to feel the strings to ensure the coil remains in place.

Risks relating to the insertion of the coil include:

  • Bleeding
  • Pain on insertion
  • Vasovagal reactions (dizziness, bradycardia and arrhythmias)
  • Uterine perforation (1 in 1000, higher in breastfeeding women)
  • Pelvic inflammatory disease (particularly in the first 20 days)
  • The expulsion rate is highest in the first three months



Before the coil is removed, women need to abstain from sex or use condoms for 7 days, or there is a risk of pregnancy. The strings are located and slowly pulled to remove the device.


Non-Visible Threads

When the coil threads cannot be seen or palpated, three things need to be excluded:

  • Expulsion
  • Pregnancy
  • Uterine perforation


Extra contraception (i.e. condoms) is required until the coil is located.

The first investigation is an ultrasound. An abdominal and pelvic xray can be used to look for a coil elsewhere in the abdomen or peritoneal cavity after a uterine perforation. Hysteroscopy or laparoscopic surgery may be required depending on the location of the coil.


Copper Coil

The copper coil (IUD) is a long-acting reversible contraception licensed for 5 – 10 years after insertion (depending on the device). It can also be used as emergency contraception, inserted up to 5 days after an episode of unprotected intercourse. It is notably contraindicated in Wilson’s disease.



Copper is toxic to the ovum and sperm. It also alters the endometrium and makes it less accepting of implantation.



  • Reliable contraception
  • It can be inserted at any time in the menstrual cycle and is effective immediately
  • It contains no hormones, so it is safe for women at risk of VTE or with a history of hormone-related cancers
  • It may reduce the risk of endometrial and cervical cancer



  • A procedure is required to insert and remove the coil, with associated risks
  • It can cause heavy or intermenstrual bleeding (this often settles)
  • Some women experience pelvic pain
  • It does not protect against sexually transmitted infections
  • Increased risk of ectopic pregnancies
  • Intrauterine devices can occasionally fall out (around 5%)


TOM TIP: The copper coil is contraindicated in Wilson’s disease. Wilson’s disease is a condition where there is excessive accumulation of copper in the body and tissues. Examiners like to add questions on this, as it requires knowledge of the copper coil and Wilson’s disease. 


Levonorgestrel Intrauterine System

There are four types of IUS you may come across, all containing levonorgestrel:

  • Mirena: effective for 5 years for contraception, and also licensed for menorrhagia and HRT
  • Levosert: effective for 5 years, and also licensed for menorrhagia
  • Kyleena: effective for 5 years
  • Jaydess: effective for 3 years


TOM TIP: The IUS to remember is the Mirena coil. It is commonly used for contraception, menorrhagia and endometrial protection for women on HRT. It is licensed for 5 years for contraception, but only 4 years for HRT. 


The LNG-IUS works by releasing levonorgestrel (progestogen) into the local area:

  • Thickening cervical mucus
  • Altering the endometrium and making it less accepting of implantation
  • Inhibiting ovulation in a small number of women


The LNG-IUS can be inserted up to day 7 of the menstrual cycle without any need for additional contraception. If it is inserted after day 7, pregnancy needs to be reasonably excluded, and extra protection (i.e. condoms) is required for 7 days.



  • It can make periods lighter or stop altogether
  • It may improve dysmenorrhoea or pelvic pain related to endometriosis
  • No effect on bone mineral density (unlike the depo injection)
  • No increase in thrombosis risk (unlike the COCP)
  • No restrictions for use in obese patients (unlike the COCP)
  • The Mirena has additional uses (i.e. HRT and menorrhagia)



  • A procedure is required to insert and remove the coil, with associated risks
  • It can cause spotting or irregular bleeding
  • Some women experience pelvic pain
  • It does not protect against sexually transmitted infections
  • Increased risk of ectopic pregnancies
  • Increased incidence of ovarian cysts
  • There can be systemic absorption causing side effects of acne, headaches, or breast tenderness
  • Intrauterine devices can occasionally fall out (around 5%)


Problematic bleeding

Irregular bleeding can occur, particularly in the first six months. This usually settles with time. Alternative causes need to be excluded where problematic bleeding continues, including a sexual health screenpregnancy test and ensuring cervical screening is up to date.

The FSRH guidelines suggest taking the combined oral contraceptive pill (COCP) in addition to the LNG-IUS for three months when problematic bleeding occurs, to help settle the bleeding.


Actinomyces-Like Organisms (ALO) on Smears

Actinomyces-like organisms are often discovered incidentally during smear tests in women with an intrauterine device (coil). These do not require treatment unless they are symptomatic. Where the woman is symptomatic (e.g. pelvic pain or abnormal bleeding), removal of the intrauterine device may be considered.


Last updated August 2020