Gender-affirming estrogen therapy route of administration and cardiovascular risk: a systematic review and narrative synthesis.

Transgender women (individuals assigned male sex at birth who identify as women) and nonbinary and gender-diverse individuals receiving gender-affirming estrogen therapy (GAET) are at increased cardiovascular risk. Nonoral (i.e., patch, injectable) compared with oral estrogen exposure in cisgender women (individuals assigned female sex at birth who identify as women) may be associated with lower cardiovascular risk, though whether this applies to transgender women and/or gender-diverse individuals is unknown. We sought to determine the association between the route of estrogen exposure (nonoral compared with oral) and cardiovascular risk in transgender women and gender diverse individuals. Bibliographic databases (MEDLINE, Embase, PsycINFO) and supporting relevant literature were searched from inception to January 2022. Randomized controlled trials and observational studies reporting cardiovascular outcomes, such as all-cause and cardiovascular mortality, adverse cardiovascular events, and cardiovascular risk factors in individuals using nonoral compared with oral gender-affirming estrogen therapy were included. The search strategy identified 3,113 studies, 5 of which met inclusion criteria (3 prospective cohort studies, 1 retrospective cohort study, and 1 cross-sectional study; = 259 participants, range of duration of exposure of 2 to 60 mo). One out of five studies reported on all-cause and cardiovascular mortality or adverse cardiovascular events. All five studies reported lipid levels [low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides (TG), and total cholesterol (TC)], whereas only two studies reported systolic blood pressure (SBP) and diastolic blood pressure (DBP). Limited studies have examined the effect of the route of GAET on all-cause cardiovascular mortality, morbidity, and risk factors. In addition, there is significant heterogeneity in studies examining the cardiovascular effects of GAET. This study is the first to summarize the potential effect of nonoral versus oral gender-affirming estrogen therapy use on cardiovascular risk factors in transgender women or nonbinary or gender-diverse individuals. Heterogeneity of studies in reporting gender-affirming estrogen therapy formulation, dose, and duration of exposure limits quantification of the effect of gender-affirming estrogen therapy on all-cause and cardiovascular mortality, adverse cardiovascular events, and cardiovascular risk factors. This systematic review highlights the needs for large prospective cohort studies with appropriate stratification of gender-affirming estrogen therapy by dose, formulation, administration route, and sufficient follow-up and analyses to limit selection bias to optimize the cardiovascular care of transgender, nonbinary, and gender-diverse individuals.