Body Mass Index Distributions and Obesity Prevalence in a Transgender Youth Cohort - A Retrospective Analysis.

Purpose: To evaluate differences in auxological parameters between transgender and cisgender adolescents.

Methods: Retrospective analysis of auxological data of 269 transgender and gender diverse patients (75% assigned female at birth or AFAB, 25% assigned male at birth or AMAB) at the outpatient clinic for Pediatric Endocrinology at the Vienna General Hospital. All were treatment naïve at initial measurement. Height and weight data were compared to current World Health Organization (WHO) standards, defining a standard deviation score (SDS) of ≥ 1 ≤ 2 as overweight and > 2 as obese.

Results: In our untreated transgender population (mean age 15.7 years), 20% were overweight and 17% obese. Mean BMI was 0.64 SDS above the WHO average (p < .001). This result was more pronounced in the AFAB subgroup (+0.73 SDS, p < .001) than in the AMAB group (+0.37 SDS, p = .07). The AMAB group showed markedly higher BMI variance compared to WHO standards (p < .001) and to the AFAB group (p = .03), due to a higher relative number of underweight observations. When correcting for psychiatric diagnosis, transgender patients were still significantly overweight (p < .001). In patients for whom data both pregender-affirming hormone therapy and during gender-affirming hormone therapy was available (n = 133), BMI SDS did not change significantly over time (p = .22).

Discussion: We observed significantly higher rates of overweight and obesity in our adolescent transgender cohort. The reasons are likely complex and multifactorial. This makes eating and exercise behaviors central in both transgender care and future research.