Impact of adenomyosis on the outcome of in vitro fertilization

We recently read an article by Wang et al. in Acta Obstetricia et Gynecologica Scandinavica . 1 The authors reviewed the available literature to quantitatively assess the impact of adenomyosis diagnosed by ultrasound on the outcome of in vitro fertilization. 1 However, this study may have some methodological flaws. In the Material and methods section, the authors emphasize a comprehensive search of only three databases, namely Embase, PubMed, and the Cochrane Library. Other commonly used databases, such as PsycINFO, Google Scholar, Web of Science, CINAHL, and Scopus were not included. Chinese databases with large volumes of literature, such as China Knowledge Network and Wanfang, were also excluded without any plausible explanation. This might have led to the omission of relevant target literature. Broadening the search could improve the validity of the results and conclusions of this systematic review. In addition, we suggest that the authors provide a detailed search procedure and present it in tabular form in the text. In the article, the authors used the Newcastle–Ottawa scale 2 to assess the quality of the studies. However, Stang has questioned the validity of this scoring tool because it is prone to highly arbitrary results. 3 Therefore, we suggest that the authors use a more valid and stable tool for quality assessment, such as the Down and Black tool. 4 Finally, most of the pooled outcomes in this meta‐analysis are highly heterogeneous, which significantly reduces the credibility of the conclusions. Although the authors tried very hard to explain the sources of heterogeneity through various subgroup analyses, this does not fully address the issue. Therefore, we suggest that the authors consider an inverse variance heterogeneity model as an alternative to the random effects model. This model could reduce the known problems of random effects models—of underestimating statistical errors and giving incorrect overconfidence estimates—and so reflect the true magnitude of the effect of the results. 5 Despite these shortcomings, this study may have a positive impact on current clinical practice guidelines. Future high‐quality randomized controlled trials with larger sample sizes are needed to further confirm the conclusions of this systematic review and meta‐analysis.