Abstract
Miscarriage, the loss of a pregnancy before viability, can be sporadic or recurrent. Emerging evidence links miscarriage to specific microbiota compositions within the female reproductive tract (FRT). This systematic review aims to synthesise evidence on the association between sporadic and recurrent miscarriage and FRT microbiota composition, as assessed using metataxonomic profiling approaches. A systematic analysis of the 43 included studies, sampling the vaginal, cervical and endometrial microbiota supported an association between reduced Lactobacillus abundance and miscarriage, making it a potential target for therapeutic intervention. However, consistent changes in alpha and beta diversity were not observed and there was a lack of reproducibility for other compositional changes. This review also highlighted concerns about the significant bias introduced due to methodological variations and emphasises the need for future standardisation of microbial sampling, sequencing, and reporting to allow accurate comparison of results and to reduce research waste.
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No new datasets were generated or analysed during the current study. The data used to support the findings of this study are available from the corresponding author upon request.
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This is available from https://osf.io/9scwe/files/8na5e.
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Acknowledgements
No direct funding was received for this work. N.B. and S.Q. are supported by Efficacy and Mechanism Evaluation Programme, an MRC and NIHR Partnership (Reference: 17/60/22). I.H. is supported by an MRC fellowship. J.O. is an NIHR Academic Clinical Lecturer. S.Q. and D.A.M. are supported by the Tommy’s National Centre for Miscarriage Research. D.A.M. is supported the March of Dimes.
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N.B. conceived the project. All authors contributed to the development of the protocol. N.B., I.H. and J.O. performed study selection and data extraction. N.B. performed the data analysis and completed the first draft of the manuscript. All authors (N.B., I.H., J.O., S.Q. and D.A.M.) reviewed and revised the manuscript.
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N.B., I.H., S.Q. and J.O. have no competing interests to declare. D.A.M. holds a patent for the use of Lactobacillus crispatus CTV-05 in the prevention of preterm birth (US63/151474).
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Black, N., Henderson, I., Quenby, S. et al. Microbiota composition of the female reproductive tract and miscarriage: a systematic review and meta-analysis. npj Biofilms Microbiomes (2026). https://doi.org/10.1038/s41522-025-00901-9
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DOI: https://doi.org/10.1038/s41522-025-00901-9
