(225) Microbiome Composition and Functional Diversity of the Vaginal Microenvironments in Women with Abnormal Uterine Bleeding

Introduction Abnormal uterine bleeding (AUB) is a pathological condition defined by irregularities in the frequency, duration, volume, or regularity of uterine bleeding, affecting 10–30% of reproductive-age women in Korea. Although the role of the microbiome in gynecological health has gained increasing attention, investigations specifically examining vaginal microbiota alterations in AUB remain limited. Objective To characterize the vaginal microbiota in women with abnormal uterine bleeding (AUB) and assess differences according to etiologic subgroups. Methods This prospective observational study included 176 premenopausal women with AUB and 100 healthy controls. The vaginal microbiota was analyzed using 16S rRNA gene sequencing. Main outcome measures included alpha and beta diversity, community state types (CSTs), taxonomic composition, and microbial co-occurrence networks. AUB etiologies were categorized according to the FIGO PALM-COEIN classification system to allow for subgroup analysis (structural-benign, structural-malignant, and non-structural). Results Women with AUB exhibited significantly higher alpha diversity and distinct beta diversity compared to controls (p < 0.01). CST IV, characterized by low Lactobacillus and high anaerobic diversity, was predominant in the AUB group (57.4%), whereas CST I (L. crispatus-dominant) was most common in healthy controls (47.0%). Genera enriched in AUB included Gardnerella, Atopobium, Prevotella, Sneathia, Ralstonia, and Streptococcus. Subgroup analyses showed an enrichment of Prevotella and Mycoplasma_g19 in malignancy-associated AUB, which also had greater microbial diversity compared to benign cases. Microbial co-occurrence networks were sparse in healthy, benign, and malignant AUB groups, but the network for non-structural AUB was denser and more modular. Within this network, Fusobacterium emerged as a central hub taxon. Conclusions AUB is associated with distinct alterations of the vaginal microbiota, including CST IV predominance, reduced Lactobacillus, and an enrichment of anaerobic taxa. Subgroup-specific differences, such as increased diversity in malignancy-associated AUB and a Fusobacterium-centered network in non-structural AUB, were observed. These findings suggest a potential role for microbial dysbiosis in AUB pathogenesis and warrant validation in larger, well-controlled cohorts to determine their clinical significance. Disclosure No