Differences in Vaginal Microbiota Composition Between Infertile and Fertile Patients: A Prospective Study

<b>Background/Objectives</b>: Dysbiosis of the vaginal microbiota, particularly the loss of Lactobacillus spp. dominance, is linked to female infertility. While community state types (CSTs) I-III and V have been studied extensively, CST IV remains underexplored. The aim of this prospective study was to compare vaginal microbiota composition-specifically CST IVA and IVB-between fertile and infertile women. <b>Methods</b>: Vaginal samples were collected from 22 women (15 infertile, 7 fertile) using cervical brushes and analyzed via 16S rRNA gene sequencing. DNA was extracted, and V3-V4 regions were sequenced using the Illumina MiSeq platform. Taxonomic classification was performed with QIIME 2 and the Greengenes database. Differences in microbial composition were assessed using the Wilcoxon rank-sum test (<i>p</i> < 0.05) in SPSS v21.0. <b>Results</b>: Infertile women showed lower relative abundances of <i>Lactobacillus</i> spp. (31.54% vs. 42.32%) and <i>Oscillospira</i> spp. relative to fertile women. CST IV was more frequent in the infertile group (29.75% vs. 21.61%). Within CST IV, CST IVA accounted for a higher proportion in infertile women (7.0% vs. 0.94%), with <i>Prevotella</i> spp. representing 95.18% of CST IVA in infertile subjects, as opposed to the figure of 69.77% in fertile counterparts. No clear differences in CST IVB were observed between groups. <b>Conclusions</b>: Increased prevalence of <i>Prevotella</i> spp. in CST IVA may contribute to an unfavorable vaginal environment in infertile women, potentially affecting sperm viability. The presence of <i>Oscillospira</i> spp. in fertile women suggests it is associated with a healthy vaginal microbiota profile.