The gut-endometrium axis in chronic endometritis: the role of bacterial translocation, the estrobolome, and estrogen metabolism - A narrative review.

Chronic endometritis (CE) is an inflammatory endometrial finding associated in some studies with recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL), although diagnostic thresholds and clinical significance remain unsettled. This narrative review examines whether gut dysbiosis, microbial-product translocation, and microbial estrogen metabolism could plausibly influence CE. PubMed/MEDLINE was searched to identify illustrative human, translational, and experimental literature; selection was purposive and no systematic-review protocol, formal screening, risk-of-bias assessment, or meta-analysis was undertaken. Human studies published in 2024 report associations between CE and altered endometrial or vaginal microbial profiles, but they do not establish a causal gut-endometrium pathway. Evidence for intestinal permeability, circulating lipopolysaccharide, estrobolome-mediated estrogen changes, progesterone resistance, or microbiome-directed treatment specifically in CE is indirect or preclinical. We therefore present the gut-endometrium axis as a hypothesis-generating conceptual framework rather than an established mechanism. Current evidence does not support routine gut microbiome testing, permeability biomarkers, probiotics, fecal microbiota transplantation, or hormone modification for CE. Prospective studies using standardized CE criteria, contamination-aware microbiome methods, direct gut and endometrial sampling, and reproductive outcomes are required before clinical implementation.