There is little direct evidence of the risks posed by intrauterine devices (IUDs) used for emergency contraception. The main risks are a small (< 1 in 100) and transient risk for chlamydial pelvic inflammatory disease, and a small (< 1 in 1000) risk that the uterus will be perforated when the IUD is inserted.

The National Institute for Health and Clinical Excellence has reviewed the evidence on the safety of IUDs used for long-acting contraception [National Collaborating Centre for Women's and Children's Health, 2005]. As the risks posed by IUDs are likely to be similar whether they are used for emergency contraception or long-acting contraception, the findings from the NICE guidance on long-acting reversible contraception are reviewed below.

Risks posed by intrauterine devices

• Risk of ectopic pregnancy
• The risk of ectopic pregnancy when using copper IUDs for ongoing regular contraception is lower than when using no contraception.
• The absolute risk of ectopic pregnancy when using the IUD is very low: about 1 in 1000 IUD users over 5 years.
• However, the relative risk (RR) of an ectopic pregnancy is increased in women who fall pregnant with an IUD still in place: about 50 in 1000 pregnancies compared with about 14 in 1000 pregnancies for women using no contraception.
• Risk of pelvic inflammatory disease
• There is concern that inserting an IUD may introduce an infection (e.g. Chlamydia), if one is present, into the upper genital tract and thus cause pelvic inflammatory disease.
• The risk of developing pelvic inflammatory disease after IUD insertion is very low (less than 1 in 100) in women who are at low risk of sexually transmitted infections:
• A review of 12 randomized controlled studies (n = 22,908 IUD insertions, 51,399 woman-years of follow up) reported an incidence of pelvic inflammatory disease of 1.6 per 1000 woman-years, whichever type of IUD was used.
• The risk of pelvic inflammatory disease was greater for the first 3 weeks after an IUD was inserted (RR 6.30, 95% CI 3.42 to 11.6).
• The risk of pelvic inflammatory disease was greater in women younger than 25 years (RR 2.45, 95% CI 1.36 to 3.85).
• A systematic review published after the NICE guidance reported similar results from 6 studies [Mohllajee et al, 2006].
• The absolute risk of pelvic inflammatory disease was low: 0–5% for women with chlamydial infection or gonorrhoea at the time of IUD insertion, and 0–2% for those without a sexually transmitted infection.
• Risk of perforation of the uterus
• An uncommon but serious complication of IUD insertion is perforation of the uterus. This is usually caused by the IUD itself, and less commonly caused by the sound (i.e. the rod) used to measure the length of the uterus.
• Observational studies with almost 56,000 participants found the risk of uterine perforation to be less than 1 in 1000 insertions of an IUD.
• The incidence of clinically important perforation is probably an underestimate of total perforations, as many perforations probably go unrecognized and events not requiring hospital treatment may not have been reported.
• Experts suggest that the risk of perforation is higher with less-skilled operators.
• Risk of miscarriage in women who fall pregnant with an IUD in place
• Miscarriage is the most frequent complication. Up to 60% of intrauterine pregnancies will miscarry if the IUD is not removed; for women pregnant under normal circumstances, the risk of miscarriage is about 13%.
• Risk of reduced fertility after removal of an IUD
• An early study suggested that, after removal of an IUD, women might find it more difficult than expected to fall pregnant; subsequent studies with more careful control of possible biases (for example, pre-existing or history of sexually transmitted infections) failed to confirm that return to fertility is an important risk.
• Risk of endocarditis
• There is concern that placing an IUD could result in endocarditis in women with prosthetic cardiac valves or recent endocarditis. However, no evidence supports this theoretical risk. One small study identified transient bacteraemia from vaginal organisms in 13% of women within 10 minutes of IUD replacement or insertion.

[National Collaborating Centre for Women's and Children's Health, 2005]