Dysbiosis in PCOS: A Systematic Review of Microbiome Alterations Across Body Sites with GRADE Assessment of Evidence Quality

Polycystic Ovary Syndrome (PCOS) is a prevalent endocrine-metabolic disorder that adversely affects reproductive, metabolic, and cardiovascular health in females, leading to menstrual irregularities and an increased risk of endometrial malignancies. Emerging research evidence suggests that the gut and extra gastrointestinal microbiome dysbiosis may play a significant role in the pathophysiology of PCOS. This systematic review aims to elucidate the microbiome dysbiosis patterns in PCOS patients compared to healthy controls. A systematic search was conducted across PubMed, Scopus, and Web of Science from inception until February 28 th , 2025, encompassing all original cross-sectional, cohort, or case-control studies that examined the gut, oral, blood, and lower genital tract (LGT) microbiomes of PCOS patients (cases) against healthy females (controls). Of the 4,377 studies identified, 64 were assessed for eligibility through full-text screening, and ultimately, 29 studies met inclusion criteria and were included into the systematic review. The results revealed inconsistent patterns in alpha and beta diversity, with reports of increased, decreased, or unchanged microbial diversity across studies. Key alterations were observed at different taxonomic levels, such as phylum, family, genus, and species. The most significant bacterial alterations include changes in the relative abundance of various bacterial taxa such as Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria, Verrucomicrobia, Gammaproteobacteria, Fusobacteria, Eubacterium, Streptococcus, Paraprevotella, Tucibacter, and Tenericutes. These findings indicate that complex dysbiotic microbial shifts may be involved in the pathogenesis of PCOS. As per the GRADE assessment, the quality of evidence is low for most of the studies. This systematic review supports the role of microbial dysbiosis in PCOS pathogenesis, however, additional research is required to elucidate these interactions to guide the development of therapeutic strategies in the future.