IUD use and the risk of ectopic pregnancy: a meta-analysis of case-control studies

CRD COMMENTARY: This is a thoughtful, well-written and clearly-presented review. By limiting the literature search to published articles some relevant studies may have been omitted. Predefined forms were used to assess study quality according to specified criteria, but no details are given of the methodology used to select studies for inclusion, to assess quality or to extract data. The potential bias inherent in quality assessment is acknowledged by the authors. Sensitivity analysis investigated the effect of the quality of the studies on the results, and assessed the influence of confounding factors. Details were lacking on the diagnostic criteria used to define ectopic pregnancy and the length of follow-up period after insertion of the IUD. The complexities of selecting an appropriate control group for case-control studies of ectopic pregnancies are discussed in detail, as are the potential influences of various factors on the incidence of ectopic pregnancy, e.g. the different types of IUD and the increasing use of more effective medicated IUDs. The authors comment that although they found no statistical differences between different IUD types, it was impossible to analyse the innovation in IUDs in recent years with respect to the risk of ectopic pregnancy, due to lack of information about the type of IUD and the problems of recall bias. Potential causes of heterogeneity between studies such as study quality, IUD type, health and socioeconomic conditions, contraceptive use, abortion, and ethnic and behavioural differences were included in the discussion.