BACKGROUND: 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.

AIM: We investigated pubertal growth, serum IGF-I and IGFBP-3, and adult height of transgender adolescents receiving hormone therapy.

METHODS: Observational study of a national cohort (2016-2023) comprising 219 transgender adolescents <18 years of age. Treatment consisted of gonadotropin-releasing hormone agonist (GnRHa) combined with estradiol or testosterone (adjusted to serum concentrations between 0 and +2 standard deviations (SDs) corresponding to the gender identity).

RESULTS: 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 SDS declined during oral estradiol administration (-0.13 SDS per month, p=0.059, and -0.02 SDS, p=0.001, respectively). We observed significantly lower adult height compared to target height for trans girls (-2.7 cm, p=0.01), and significant differences between height SDS before treatment and at adult height (-0.35 SDS, p<0.001).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<0.001).

DISCUSSION AND CONCLUSION: 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.