What is the role of chronic endometritis in implantation failure?

The evidence base for treating chronic endometritis has weakened substantially, and this needs stating plainly. ASRM (2026), addressing RPL, reports a high-quality randomised controlled trial in which 438 women with RPL and biopsy-confirmed chronic endometritis were randomised to two weeks of doxycycline or placebo, and which demonstrated no significant difference in miscarriage or live birth rate. ASRM's summary position is that this shows no benefit from prescribing doxycycline for chronic endometritis in RPL patients. That reverses the earlier direction of travel, which rested on observational data and a meta-analysis suggesting improved live birth where a test-of-cure biopsy confirmed resolution. Diagnosis, where it is performed: endometrial biopsy with plasma cell identification. There is no consensus on the plasma cell count required. One case-control study suggests the best-performing criterion is 3 or more plasma cells per whole section, or 2 or more per 10 high-power fields, using CD138 staining. Ask your histopathology service which threshold they apply, because prevalence estimates range from 7% to 57% largely on that basis. Practical position: for RPL, the randomised evidence does not support test-and-treat. For recurrent implantation failure with concurrent infertility the population differs and the question is less settled, but the RPL result should temper confidence there too. Where plasma cells accompany a polyp, polypectomy is likely sufficient without antibiotics.