Changes in Diagnostic Methods, Criteria, and Treatment for Chronic Endometritis After National Health Insurance Coverage of Assisted Reproductive Technology in Japan: A Nationwide Follow‐up Survey ( <scp>IZANAMI</scp> Project)

AIM: To evaluate how diagnostic methods, criteria, and treatment for chronic endometritis (CE) changed in Japan after introducing health insurance coverage of assisted reproductive technology (ART). METHODS: We conducted two nationwide, web-based facility surveys targeting all 616 registered ART facilities. The surveys were administered before ART insurance coverage (December 2021 to February 2022) and after coverage (December 2023 to January 2024). Facilities that responded to both surveys (283 facilities) were included. We evaluated whether facility-level CE diagnostic methods, CD138-positive plasma cell cutoff values, and first- and second-line treatment choices changed between surveys. RESULTS: CE testing was implemented by 238 facilities in the precoverage and 244 postcoverage periods. The adoption of diagnostic methods did not significantly change. Although the overall number of facilities that adopted CD138 immunohistochemical staining was stable (145 vs. 149 facilities), 23 facilities discontinued CD138 staining postcoverage while 27 newly introduced it; discontinuation occurred predominantly in clinics (91.3%), whereas 44% of new adopters were hospitals/university hospitals (p < 0.001). The cutoff value of CD138-positive cells (6-10 cells/20 high-power fields) increased between the surveys (p = 0.01). Doxycycline remained the first-line therapy. Regarding second-line therapy, ciprofloxacin plus metronidazole remained the most frequent, while probiotics significantly increased (p = 0.005). CONCLUSIONS: After ART insurance coverage in Japan, overall CE diagnostic methods and CD138 adoption remained largely unchanged. However, facilities tended to adopt higher CD138 cutoff values and treatment selections shifted. Establishing unified diagnostic criteria and treatment protocols is warranted to support standardized CE care for future health insurance coverage.