Venous Thrombotic Risk in Transgender Women Undergoing Estrogen Therapy: A Systematic Review and Metaanalysis

Transgender women are female individuals who were recorded men at birth based on natal sex. Supporting a person's gender identity improves their psychological health, and gender-affirming hormones reduce gender dysphoria and benefit mental health. For transgender women, estrogen administration has clinically significant benefits. Previous reviews have reported conflicting literature on the thrombotic risk of estrogen therapy in transgender women and have highlighted the need for more high-quality research.

To help address the gap in understanding thrombotic risk in transgender women receiving estrogen therapy, we performed a systematic literature review and metaanalysis. Two evaluators independently assessed quality using the Ottawa Scale for Cohort Studies. The Poisson normal model was used to estimate the study-specific incidence rates and the pooled incidence rate. Heterogeneity was measured using Higgins I ² statistic. The overall estimate of the incidence rate was 2.3 per 1000 person-years (95% CI, 0.8-6.9). The heterogeneity was significant (I ² = 74%; P = 0.0039).

Our study estimated the incidence rate of venous thromboembolism in transgender women prescribed estrogen to be 2.3 per 1000 person-years, but because of heterogeneity this estimate cannot be reliably applied to transgender women as a group. There are insufficient data in the literature to partition by subgroup for subgroup prohibiting the analysis to control for tobacco use, age, and obesity, which is a major limitation. Additional studies of current estrogen formulations, modes of administration, and combination therapies, as well as studies in the aging transgender population, are needed to confirm thrombotic risk and clarify optimal therapy regimens.