The interplay between vaginal microbiota and immune system in recurrent pregnancy loss and repeated implantation failure.

Recurrent pregnancy loss (RPL) and repeated implantation failure (RIF) are significant reproductive challenges globally. Emerging evidence indicates that an imbalance in the vaginal microbiota significantly impacts the immune system, potentially leading to RIF and RPL. By searching databases PubMed/MEDLINE and Google Scholar by using relevant keywords and MeSH up to August 2025, this narrative review examines recent findings on vaginal microbiota-mediated immune alterations in women experiencing RIF and RPL. Our overview demonstrated that the vaginal microbiota, specifically Lactobacillus species, plays a key role in maintaining an anti-inflammatory environment conducive to successful pregnancy. Disruption of this balance, known as vaginal dysbiosis, can induce inflammation, immune dysregulation, and activation of pathogen-response pathways, potentially resulting in pregnancy loss. Moreover, the interaction between vaginal microbiota and both innate and adaptive immunities at the molecular level offers promising avenues for developing therapeutic strategies to manage dysbiosis-induced pregnancy complications.