Association between endometriosis and chronic endometritis: A retrospective cross-sectional study.

Chronic endometritis (CE) is a plasma cell-related endometrial inflammatory phenotype that may compromise fertility, while endometriosis (EM) is an immune-mediated inflammatory disorder. However, whether EM is associated with CD138-defined CE remains uncertain. We conducted a retrospective cross-sectional study of infertile women who underwent combined laparoscopy and hysteroscopy with concomitant endometrial biopsy. EM was diagnosed and staged according to the revised American Society for Reproductive Medicine classification. And CE was defined primarily as ≥ 5 CD138⁺ plasma cells/10 HPFs, and a prespecified sensitivity analysis used ≥ 1 cell/10 HPFs. A total of 602 women were included (355 with EM and 247 without EM). CE prevalence under the primary definition was 12.7% in the EM group and 11.3% in the non-EM group (P = 0.620). In multivariable logistic regression adjusted for age, BMI, AMH, infertility type, tubal occlusion, and tubal adhesions, EM was not associated with CE (adjusted OR 1.228, 95% CI 0.723-2.085; P = 0.448), and stage-stratified analyses (I-II vs III-IV) were also non-significant. Using the ≥ 1 cell/10 HPFs cutoff yielded consistent findings (adjusted OR 0.765, 95% CI 0.542-1.079; P = 0.127). In this infertile cohort, no statistically significant association was observed between EM and CD138-defined CE.