Microbial composition across body sites in polycystic ovary syndrome: a systematic review and meta-analysis.

Polycystic ovary syndrome (PCOS) is an endocrine disorder affecting reproductive-aged women, but the cause remains unclear. Recent evidence has linked microbial composition with PCOS; however, the results are inconsistent. The aim of this systematic review was to gather current knowledge of the microbes across body sites (oral cavity, blood, vagina/cervix, gut) in women with PCOS, and meta-analyse the microbial diversity in PCOS. For this purpose, a systematic search using PubMed, Web of Science, Cochrane and Scopus was carried out. After selection, 34 studies met the inclusion criteria. Most of the studies associated changes in the microbiome with PCOS, whereas heterogeneity of the studies in terms of ethnicity, body mass index (BMI) and methodology, among other confounders, made it difficult to corroborate this relationship. In fact, 19 out of 34 of the studies were categorised as having high risk of bias when the quality assessment was conducted. Our meta-analysis on the gut microbiome of 14 studies demonstrated that women with PCOS possess significantly lower microbial alpha diversity compared with controls (SMD = -0.204; 95% CI -0.360 to -0.048; P = 0.010; I2 = 5.508, by Shannon Index), which may contribute to the development of PCOS. Nevertheless, future studies should specifically overcome the shortcomings of the current studies by through well planned and conducted studies with larger sample sizes, proper negative and positive controls and adequate case-control matching.