Effect of puberty suppression and gender affirming hormone treatment depends upon prior extent of pubertal development in young transgender adolescents.

Background: It is not known whether the extent of pubertal development influences the treatment effects in very young transgender people undergoing puberty suppression (PS) and gender-affirming hormone therapy (GAHT). This study aimed to investigate how anthropometric parameters and body composition change according to birth-assigned sex and affirmed gender during PS and GAHT.

Methods: This retrospective study included data from 201 adolescents starting PS under 15yr at a national gender service (139 trans boys and 62 trans girls). Data from 127 of them who subsequently received GAHT were available. Height, weight, BMI, total lean, fat and muscle mass (LM, FM and MM) were collected using Tanita body composition analyzer.

Results: 'In puberty' trans boys (Tanner stage 2-3), total FM increased on PS (2.49 kg, 95% CI 1.66;3.33) similarly to LM (2.41 kg, 95% CI 1.85;2.97), while in 'completing puberty' trans boys (Tanner stage 4-5) the increase of total FM (1.80 kg, 95% CI 1.21;2.39) was higher than total LM (0.97 kg, 95% CI 0.63;1.30). 'In puberty' trans boys showed increasing mean FM z-scores from baseline after 3 years of PS (from 0.70 to 1.2). Mean LM z-scores decreased in both 'in puberty' (from 0.98 to 0.5) and 'completing puberty' (from 1.16 to 0.80) trans boys. During GAHT, 'in puberty' trans boys showed a greater increase of total LM and MM (respectively 6.28 kg, 95% CI 3.54;9.02 and 6.08 kg, 95% CI 3.64;8.51). Both groups 'in puberty' and 'completing puberty' trans boys did not show a further increase in total FM. In contrast, 'completing puberty' trans girls showed the greatest increase of total FM during PS (4.27 kg, 95% CI 1.50;7.03). MM and LM % decreased throughout PS in all trans girls, whereas body composition only changed slightly during GAHT.

Conclusions: The effect of PS on body composition is more pronounced in 'in puberty' trans adolescents, and 'in puberty' trans boys are more responsive to GAHT, showing greater increases in MM and LM. In trans girls, the most significant increase in FM, along with reduction in LM and MM, occurs during PS, whereas no substantial changes were observed during subsequent GAHT. This suggests that any effect on physical performance may depend on pubertal development at the start of intervention.