Risk factors for IUD failure: results of a large multicentre case-control study.

Background: This study was conducted to identify the risk factors for intrauterine device (IUD) failure.

Methods: A retrospective case-control study was carried out between 1999 and 2002. Cases (women with an IUD and a confirmed pregnancy) and controls (women with an IUD and who were not pregnant) were recruited by gynaecologists. An anonymous questionnaire was filled in during the consultation, with specific items regarding any type of drugs used before the predicted fertile period for cases and within the cycle that ended in menses for controls.

Results: Two hundred and sixteen cases were compared with 657 controls. Age was associated with IUD failure, with a significantly lower failure risk in women>35 years. A significant relationship was observed between a history of IUD expulsion and IUD failure risk (age-adjusted odds ratio 3.31, 95% CI 1.40-7.81). No relationship was observed between the risk of IUD failure and gynaecological background (fibroma, polyps and miscarriage), nor with any type of medicine taken by the woman.

Conclusion: This study is clearly reassuring, as we found that anti-inflammatory drugs and any other medicines taken by the woman were not implicated in IUD failure. Only a history of previous IUD expulsion was found to be a risk factor for failure, indicating that these women should have regular medical and echographical follow-up. Comparing the efficacy rate of various types of IUDs, we found a clear advantage for levonorgestrel-releasing devices.