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.