Risk of endometrial polyps in women with endometriosis: a meta-analysis

Background: Endometrial polyps (EP) and endometriosis are both estrogen-dependent overgrowths of the endometrium. Several studies have shown a higher frequency of EP in endometriosis patients when compared with women without endometriosis. Therefore, we performed a meta-analysis to investigate the risk of EP in women with endometriosis. Methods: This meta-analysis searched for articles published between 1964 and 2014 in PubMed, Embase, and Cochrane Library, as well as in Chinese databases, including CNKI, VIP and Wanfang, regarding the association between endometriosis and EP. Nine cohort studies and one case-control study including 2896 women were included in this meta-analysis. The EP risk was evaluated using relative risk (RR) with a 95 % confidence interval (CI). Heterogeneity, small study effect and publication bias were assessed using Higgins I-2, sensitivity analysis and funnel plots, respectively. Results: The risk of EP increased in women with endometriosis compared with those without endometriosis (the pooled RR, 2.81; 95 % CI, 2.48-3.18). No significant heterogeneity, small study effect or publication bias was found. The risk of EP slightly increased in women with endometriosis at stages 2-4 compared with those at stage 1 (Pooled effect size: stage 2 versus stage 1, RR, 1.22, 95 % CI, 1.04 -1.42; stage 3 versus stage 1, RR, 1.23, 95 % CI, 1.06-1.42; stage 4 versus stage 1, RR, 1.29, 95 % CI, 1.11-1.51; stages 2-4 versus stage 1, RR, 1.24, 95 % CI, 1.10-1.40); however, no significantly different risk of EP in women with endometriosis existed between the other stages. Conclusion: The results suggest that it is important to identify whether patients with endometriosis also have EP and then remove any coexisting EP via hysteroscopy, especially for infertile patients. This process will be clinically helpful to treat endometriosis-related infertility in patients with endometriosis, especially for those with endometriosis that is more serious than stage 1.