The Impact of Testosterone Therapy on the Vaginal Microbiota of Transgender Men and Non-Binary People: A Prospective Study

Background Understanding the impact of testosterone on the vaginal microbiota of transgender men (TGM) and non-binary people assigned female sex at birth over time is imperative as vaginal dysbiosis and incident bacterial vaginosis (iBV) may cause bothersome genital symptoms and increase HIV/STI acquisition risk. We investigated shifts in the composition of the vaginal microbiota over time in TGM initiating testosterone for gender-affirming hormone therapy, including development of vaginal dysbiosis and iBV. Methods Participants ages ≥18 years, assigned female sex at birth and reporting TGM or non-binary identity, interested in starting injectable testosterone, demonstrating optimal vaginal microbiota, with no current STI(s) were enrolled. Participants self-collected daily vaginal specimens for 7 days prior to testosterone initiation and 90 days thereafter for vaginal Gram staining and 16S rRNA gene sequencing. Episodes of vaginal dysbiosis and iBV were defined as Nugent scores ≥4 or ≥7, respectively, each for ≥2 consecutive days. Results Between February 2022-November 2023, 9 participants enrolled, 89% (8/9) developed ≥1 episode(s) of vaginal dysbiosis after testosterone initiation, and 56% (5/9) developed iBV. Among those who developed iBV, most did so between days 20-40 after testosterone initiation. Community state type (CST) I was found most often in participants who did not develop iBV and CST IV-B most often in participants who developed iBV. Sexual activity and menses also appeared to influence the development of iBV. Conclusion The majority of participants developed vaginal dysbiosis including iBV.. Additional studies with larger sample sizes are needed to further elucidate how testosterone impacts the vaginal microbiota.