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

Background/Objectives: 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. Methods: 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 (p < 0.05) in SPSS v21.0. Results: Infertile women showed lower relative abundances of Lactobacillus spp. (31.54% vs. 42.32%) and Oscillospira 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 Prevotella 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. Conclusions: Increased prevalence of Prevotella spp. in CST IVA may contribute to an unfavorable vaginal environment in infertile women, potentially affecting sperm viability. The presence of Oscillospira spp. in fertile women suggests it is associated with a healthy vaginal microbiota profile.