Correlation between endometriosis and chronic endometritis

This single-center retrospective cohort study included infertile patients treated between October 2019 and December 2024, comparing an endometriosis (EMS) cohort (n = 250, laparoscopically and histopathologically confirmed) with a control cohort (n = 750, tubal-factor infertility only, EMS excluded by laparoscopy). All patients underwent laparoscopy, hysteroscopy, and endometrial biopsy; chronic endometritis (CE) was diagnosed by cluster of differentiation 38/cluster of differentiation 138 immunohistochemistry, and EMS was staged by revised American Society for Reproductive Medicine. CE detection rate was significantly higher in the EMS cohort than in controls (P < .001). Within the EMS cohort, CE prevalence was 45.1% in moderate-to-severe (stage III–IV) disease versus 24.0% in mild (stage I–II) disease (P = .001). Factors independently associated with concurrent CE were moderate-to-severe EMS, repeated intrauterine procedures, infertility duration ≥ 3 years, chronic pelvic pain, and higher gravidity (all P < .05). At 1 year, the EMS cohort had a lower clinical pregnancy rate (70.0% vs 80.0%), higher persistent infertility rate (30.0% vs 20.0%), and higher early pregnancy loss rate (16.0% vs 9.2%) than controls (all P < .05). Within the EMS cohort, concurrent CE was associated with a lower clinical pregnancy rate (56.0% vs 76.0%), higher persistent infertility rate (44.0% vs 24.0%), and higher early pregnancy loss rate (31.0% vs 11.3%) than EMS alone (all P = .002). These findings demonstrate a significant cross-sectional association between EMS and CE, with higher CE detection in advanced-stage EMS; however, causality and temporal sequence cannot be determined, reproductive outcomes were exploratory and unadjusted, and this single-center retrospective dataset is insufficient to support universal diagnostic or therapeutic guidelines.