SYSTEMATIC REVIEW OF THE ASSOCIATION BETWEEN VAGINAL MICROBIOME COMPOSITION AND THE SUCCESS OF FROZEN EMBRYO TRANSFER
DOI:
https://doi.org/10.71000/q57vbs63Keywords:
Vaginal Microbiome, Frozen Embryo Transfer, Infertility, Implantation, Lactobacillus, Systematic ReviewAbstract
Background: Infertility remains a significant global health burden, with frozen embryo transfer (FET) constituting an increasingly prevalent and successful assisted reproductive technology. Despite advancements, implantation failure persists, prompting investigation into the endometrial microenvironment. The vaginal microbiome is a dynamic component of this environment, yet its specific association with FET outcomes remains inconsistently reported, necessitating a systematic synthesis of the evidence.
Objective: This systematic review aims to synthesize the available evidence linking specific vaginal microbiome compositions to implantation and clinical pregnancy rates in individuals undergoing frozen embryo transfer.
Methods: Following PRISMA guidelines, a comprehensive search of PubMed/MEDLINE, Scopus, Cochrane Library, and Web of Science was conducted for observational studies published between 2014-2024. Eligible studies reported on vaginal microbiome composition prior to or during an FET cycle and its association with reproductive outcomes. Two independent reviewers performed study selection, data extraction, and quality assessment using the Newcastle-Ottawa Scale.
Results: Eight observational studies (n=1,347 participants) were included. A key finding was methodological divergence: studies using molecular sequencing (16S rRNA) consistently associated a Lactobacillus-dominant microbiome, particularly with L. crispatus, with significantly higher clinical pregnancy rates. Conversely, studies utilizing Nugent scoring found no significant association between bacterial vaginosis-defined dysbiosis and FET outcomes.
Conclusion: The association between vaginal microbiome and FET success appears contingent on assessment methodology. An optimal microbiome, characterized by specific beneficial lactobacilli, may support implantation, whereas traditional diagnostic criteria lack sensitivity for this predictive role. Current evidence, while promising, is observational and heterogeneous. Future research requires standardized molecular methodologies and randomized controlled trials to explore causal relationships and therapeutic modulation.
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Copyright (c) 2025 Fatima Noor, Mah Noor Khan, Mahin Aftab, Farhat R Malik, Aisha Ali, Muniba Ali, Zarina Naz (Author)
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