Chronic endometritis diagnosed using a cut-off of ≥5 CD138 plasma cells significantly affects the reproductive outcomes of frozen embryo transfer: a case-control study

OBJECTIVE: To investigate the clinical significance of a diagnosis of chronic endometritis (CE) made using a diagnostic cut-off of ≥1 or ≥5 CD138 plasma cells per high power field (HPF) in asymptomatic patients undergoing in vitro fertilization (IVF) with frozen embryo transfer (FET). MATERIAL AND METHODS: In this retrospective case-control study, 1,865 patients underwent freeze-all-IVF treatment between January and December 2019, with 419 undergoing endometrial biopsies at oocyte retrieval. Of the 419 biopsy-patients, 301 have since undergone first FET. The processed endometrial biopsies of the 301 patients underwent immunohistochemical (IHC) examination with anti-CD138 to count CD138+ plasma cells per HPF. CE diagnosis was defined as 0 CD138 plasma cells (control-group), ≥1 CD138 plasma cells (CE(control)-group) or ≥5 CD138 plasma cells (CE(disease)-group) per HPF. RESULTS: Twenty-six (8.6%) patients were retrospectively diagnosed having ≥1 CD138 plasma cells, and five patients (1.7%) having ≥5 CD138 plasma cells (CE(disease)-group) per HPF. The live birth and pregnancy loss rates of the three groups were 52.7% and 27.9%, 53.8% and 26.3% and 20.0% and 66.7%, respectively. The antral follicle count (AFC) of the three groups were 15.0 (9.0-22.0), 10.5 (7.75-15.25), and 6.0 (5.0-14.0), respectively. CONCLUSION: Asymptomatic patients diagnosed with CE with ≥5 CD138 plasma cells per HPF, had the lowest live birth and highest pregnancy loss rates, with these patients also having significantly reduced AFC.