Unraveling the intricate link: gut microbiota and recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) affects 1%-5% of reproductive-age couples, and nearly 50% of cases remain unexplained. This review summarizes recent evidence to elucidate the association between gut microbiota dysbiosis and RSA. We confirm that RSA patients exhibit decreased alpha diversity, reduced levels of Bacteroidetes, Lactobacillus, and Bifidobacterium, and elevated Proteobacteria and Escherichia-Shigella. Gut dysbiosis contributes to RSA through three core pathways: disrupted T helper 17/regulatory T cell balance leading to maternal-fetal immune intolerance; insufficient short-chain fatty acid production and elevated trimethylamine N-oxide causing metabolic disorders; and disrupted estrogen and progesterone metabolism via microbial hydroxysteroid dehydrogenases triggering endocrine dysfunction. We also clarify the bidirectional causal relationship between gut dysbiosis and RSA, summarize inconsistent findings across studies, and highlight the potential of probiotics and dietary interventions. This review provides mechanistic insights and clinical implications for microbiota-targeted strategies in unexplained RSA.