Transgender Girls Grow Tall: Adult Height Is Unaffected by GnRH Analogue and Estradiol Treatment

CONTEXT: Transgender adolescents can receive gonadotropin-releasing hormone analogues (GnRH) and gender-affirming hormone therapy (GAHT), but little is known about effects on growth and adult height. This is of interest since height differs between sexes and some transgender girls wish to limit their growth. OBJECTIVE: This work aims to investigate the effects of GnRHa and GAHT on growth, and the efficacy of growth-reductive treatment. METHODS: This retrospective cohort study took place at a specialized tertiary gender clinic. A total of 161 transgender girls were treated with GnRHa and estradiol at a regular dose (2 mg) or high growth-reductive doses of estradiol (6 mg) or ethinyl estradiol (EE, 100-200 µg). Main outcome measures included growth, adult height, and the difference from predicted adult height (PAH) and target height. RESULTS: Growth velocity and bone maturation decreased during GnRHa, but increased during GAHT. Adult height after regular-dose treatment was 180.4 ± 5.6 cm, which was 1.5 cm below PAH at the start GnRHa (95% CI, 0.2 cm to 2.7 cm), and close to target height (-1.1 cm; 95% CI, -2.5 cm to 0.3 cm). Compared to regular-dose treatment, high-dose estradiol and EE reduced adult height by 0.9 cm (95% CI, -0.9 cm to 2.8 cm) and 3.0 cm (95% CI, 0.2 cm to 5.8 cm), respectively. CONCLUSION: Growth decelerated during GnRHa and accelerated during GAHT. After regular-dose treatment, adult height was slightly lower than predicted at start of GnRHa, likely due to systematic overestimation of PAH as described in boys from the general population, but not significantly different from target height. High-dose EE resulted in greater reduction of adult height than high-dose estradiol, but this needs to be weighed against possible adverse effects.