Just as Tall on Testosterone; a Neutral to Positive Effect on Adult Height of GnRHa and Testosterone in Trans Boys

CONTEXT: Growth is an important topic for many transgender boys. However, few studies have investigated the impact of puberty suppression (PS) and gender-affirming hormone treatment (GAHT) on growth and adult height. OBJECTIVE: To evaluate the effect of PS and GAHT on growth and adult height. DESIGN: Retrospective cohort study. SETTING: Specialized gender identity clinic. PARTICIPANTS: A total of 146 transgender boys treated with GnRH analogues and testosterone who reached adult height. MAIN OUTCOME MEASURES: Growth, bone age (BA), adult height, and difference between adult height and predicted adult height (PAH) and midparental height. RESULTS: In those with BA ≤14 years at start (n = 61), a decrease in growth velocity and bone maturation during PS was followed by an increase during GAHT. Adult height was 172.0 ± 6.9 cm; height SD score was similar to baseline (0.1; 95% CI, −0.2 to 0.4). Adult height was 3.9 ± 6.0 cm above midparental height and 3.0 ± 3.6 cm above PAH at start of PS. A younger BA at start PS was associated with an adult height significantly further above PAH. CONCLUSION: During PS, growth decelerated followed by an acceleration during GAHT. Although adult height SD score was similar to baseline, adult height was taller than predicted based on BA at baseline, especially in those who started treatment at a younger BA. It is reassuring that PS and GAHT do not have a negative impact on adult height in transgender boys and might even lead to a slightly taller adult height, especially in those who start at a younger age.