Polycystic ovary Syndrome (PCOS) is one of the most popular diseases that cause menstrual dysfunction and infertility in women. Recently, the relationships between the gastrointestinal microbiome and metabolic disorders such as obesity, type 2 diabetes and PCOS have been discovered. However, the association between the gut microbiome and PCOS symptoms has not been well established. We systematically reviewed existing studies comparing gut microbial composition in PCOS and healthy volunteers to explore evidence for this association. A systematic search was carried out in PubMed, Embase, Cochrane Library, and Web of Science from inception to May 26, 2020, for all original cross-sectional, cohort, or case-control studies comparing the fecal microbiomes of patients with PCOS with microbiomes of healthy volunteers (controls). The primary outcomes were differences in specific gut microbes between patients with PCOS and controls. The search identified 256 citations; 10 studies were included. The total population study of these articles consists of 611 participants (including PCOS group and healthy controls group). Among the included 10 studies, nine studies compared α-diversity, and six studies demonstrated that α-diversity has a significant reduction in PCOS patients. Seven of them reported that there was a significant difference of β-diversity composition between healthy controls groups and PCOS patients. The most common bacterial alterations in PCOS patients included Bacteroidaceae, Coprococcus, Bacteroides, Prevotella, Lactobacillus, Parabacteroides, Escherichia/Shigella, and Faecalibacterium prausnitzii. No consensus has emerged from existing human studies of PCOS and gut microbiome concerning which bacterial taxa are most relevant to it. In this systematic review, we identified specific bacteria associated with microbiomes of patients with PCOS vs controls. Higher level of evidence is needed to determine whether these microbes are a product or cause of PCOS.
