ESPE Abstracts

Background: Linear growth during spontaneous puberty contributes approximately 20% to adult height in healthy subjects. The impact of gender-affirming hormone therapy (GAHT) on final height in transgender adolescents is sparsely studied.

Aim: We aimed to investigate the growth and final height of Danish transgender adolescents.

Methods: Our national cohort of transgender adolescents (2016-2023) comprised 167 adolescents, 38 trans girls (assigned male sex at birth) and 129 trans boys (assigned female sex at birth). They all received GAHT before the age of 18 years. Treatment consisted of Gonadotropin-Releasing Hormone agonist (GnRHa) (n=167) combined with either estradiol (n=32 trans girls) or testosterone (n=117 trans boys). Doses of estradiol and testosterone were adjusted to reach a serum concentration of estradiol or testosterone, respectively, between median and +2SD for the references of the experienced sex. Height, weight, and blood samples were collected at routine visits and compared to Danish references. Height velocities were compared to international references.

Results: Overall, adult heights were within ±2 SD for references of the sex assigned at birth in all trans girls and trans boys. Most trans girls reached adult heights within adult references of cis girls. Half of the trans boys remained short (<-2 SD) compared to cis boys. Growth velocity declined during GnRHa treatment in both trans girls and trans boys. For trans girls with a bone age below 15 years before starting GAHT, we observed a growth spurt when initiating estradiol treatment. We observed a small but significant difference between target height and adult height for trans girls (mean -3.6 cm, P=0.0022) and between height SDS before treatment and adult height for both trans girls (mean -0.31 SDS, P<0.001) and trans boys (mean -0.17 SDS, P<0.001). Serum IGF-I and IGFBP-3 concentrations were within the references for the experienced sex, and we observed a decrease in serum IGFBP-3 for the trans boys on testosterone treatment.

Discussion and Conclusion: Most transgender adolescents initiating GAHT during adolescence reached a final height within ±2 SD for sex assigned at birth. We found a subtle but significant decline in final height of trans girls treated with GnRH agonist and estradiol before 18 years of age, which may be considered beneficial by some. Whereas trans boys did not experience any height gain.