Endometriosis is a chronic inflammatory disease defined by the presence of endometrial-like tissue outside the uterine cavity. Several authors have reported on the association between changes in inflammatory marker levels and the maintenance or progression of endometriosis and associated infertility. Interleukin-6 (IL-6) is the most studied cytokine in endometriosis and has important functions in reproductive physiology. The aim of this study is to review systematically available evidence about altered IL-6 concentrations in endometriosis-related infertility. This is a systematic review including all studies until December 2022 in which IL-6 in serum, peritoneal fluid, follicular fluid, or endometrial biopsy specimens was measured and that correlated their findings with endometriosis- associated infertility. Fifteen studies were included in the systematic review. There seems to be a correlation between elevated serum and peritoneal fluid IL-6 concentrations and the occurrence of endometriosis-associated infertility. IL-6 may be a potential diagnostic or biomarker tool for the prediction of endometriosis-related infertility. However, the numerous biases affecting the available studies, and challenges in endometriosis research reproducibility must be considered. Future investigations should pay attention to factors that may affect the results, such as the choice of suitable control groups, and carefully consider other pathological conditions affecting the patients, endometriosis stage, and type of lesion.
Keywords: Endometriosis; Interleukin-6; infertility.