Shaping the skeleton: impact of GnRH analogue and sex hormone therapy on skeletal dimensions in transgender individuals.

Context: Skeletal dimensions vary between sexes. Men typically have broader shoulders and women a wider pelvis. If gender affirming hormone therapy (GAHT) with or without prior puberty suppression (PS) alters these dimensions in transgender individuals remains unclear.

Objective: To investigate impact of PS and GAHT on skeletal dimensions.

Design: Retrospective cross-sectional study.

Setting: Gender identity clinic.

Participants: Transgender individuals assigned male at birth (AMAB) and assigned female at birth (AFAB) who underwent dual-energy X-ray absorptiometry (DXA) scanning between ages 18 and 28 years were divided into four groups: Early PS (Tanner G/B2-3)+GAHT, Late PS (Tanner G/B4-5)+GAHT, GAHT only, and Untreated.

Main Outcome Measures: Shoulder and pelvis dimensions measured by DXA scan were compared between groups, with adjustment for height.

Results: A total of 121 individuals AMAB and 122 AFAB were included. Only in individuals AMAB who underwent early PS had smaller shoulders compared to untreated individuals AMAB (-1.3 cm; 95%CI -2.1; -0.5). In individuals AMAB from both the early and late PS group, pelvic inlet, pubic symphysis width and interischial distance were greater compared to untreated individuals AMAB resulting in dimensions comparable to untreated individuals AFAB. Only in early PS AFAB pelvic inlet width was smaller compared to untreated individuals AFAB (-1.0 cm; 95%CI -1.5; -0.6), and comparable to untreated individuals AMAB.

Conclusions: The study results suggest that skeletal dimensions are only altered by GAHT if endogenous puberty has not yet been completed at start of PS. These findings enhance our understanding of hormonal effects on the skeleton and may hold clinical relevance for body image as well as for forensic anthropology. Future research should evaluate clinical implications for surgical or obstetrical outcomes in transgender individuals.