Growth and Adult Height Attainment in Danish Transgender Adolescents Treated With GnRH Analog and Sex Hormones

Endogenous sex steroids influence the pubertal growth spurt and adult height. However, the impact of puberty suppression and sex steroids on growth in transgender adolescents is sparsely studied. We investigated pubertal growth, serum IGF-I and IGF binding protein-3 (IGFBP-3), and adult height of transgender adolescents receiving hormone therapy. Observational study of a national cohort (2016-2023) comprising 219 transgender adolescents <18 years of age. Treatment consisted of gonadotropin-releasing hormone agonist combined with estradiol or testosterone (adjusted to serum concentrations between 0 and +2 SDs corresponding to the gender identity). Adult height was within ±2 SD for sex assigned at birth.Most trans girls reached adult height within references of girls. For trans girls (bone age ≤15 years before treatment), a growth spurt was observed during estradiol therapy. IGF-I and height SD score (SDS) declined during oral estradiol administration (-0.13 SDS per month, P = .059, and -0.02 SDS, P = .001, respectively). We observed significantly lower adult height compared to target height for trans girls (-2.7 cm, P = .01) and significant differences between height SDS before treatment and at adult height (-0.35 SDS, P < .001).Half of the trans boys remained short (<-2 SD) compared to references for boys, and most completed growth spurt before initiation of treatment. IGFBP-3 declined following testosterone treatment. There was a significant difference between height SDS before treatment and at adult height (-0.17 SDS, P < .001). The minor reduction in adult height of trans girls after hormone treatment may be beneficial to some, whereas trans boys did not experience height gain.