Characteristics of the Vaginal Microbiome Before and After Testosterone Treatment in Transgender Men

Purpose: Sex hormone levels affect the composition of vaginal flora. Changes in the vaginal microbiome affect overall health. Among transgender men (TM) who receive gender-affirming treatment, there can be changes in the vaginal microbiome, causing adverse effects that are usually neglected by both transgender individuals and health care professionals. This study aimed to elucidate the effect of testosterone on the vaginal microbiome. Methods: This prospective study was conducted at King Chulalongkorn Memorial Hospital, Thailand, from January 2021 to June 2023. All patients who were TM and had not received testosterone were included in the study. High-throughput sequencing was used to evaluate bacterial community profiles. Testosterone enanthate 150 mg was administered via intramuscular injection every three weeks. Vaginal health was reevaluated 12 weeks after treatment. The primary objective of this study was to compare the vaginal microbiomes before and after testosterone replacement therapy. Results: Twenty-six participants were included in this study. Compared with pre-testosterone treatment, testosterone-treated TM had a lower likelihood of having Lactobacillus spp. as the dominant bacterial species, a considerably higher relative bacterial abundance of various species, and higher alpha diversity ( p < 0.01). Clinically, after administering testosterone for 12 weeks, the participants reported more symptoms ( p = 0.04), higher vaginal atrophy scores ( p < 0.01), a lower normal flora index ( p < 0.01), higher vaginal pH ( p < 0.01), and worse scores for vaginal maturation values ( p < 0.01). Conclusion: The use of testosterone in TM may alter the vaginal microbiota by decreasing Lactobacillus colonization and increasing alpha diversity. The Clinical Trials Registration number is TCTR20210202007 (Thai Clinical Trials Registry).