What are the health outcomes of trans and gender diverse young people in Australia? Study protocol for the Trans20 longitudinal cohort study.

Introduction Being transgender is frequently accompanied by gender dysphoria, which often coexists with mental health concerns. Increased referrals of transgender and gender diverse (TGD) youth to gender clinics have been observed in many countries. Nevertheless, there are limited empirical data on the presentation and outcomes of these patients, and there is an urgent need for more evidence to ensure optimal medical and psychosocial interventions. Here, we describe Trans20, a longitudinal study of TGD patients attending a multidisciplinary paediatric gender service in Melbourne, Australia. Trans20 aims to understand the demographic and clinical characteristics of these patients, to document the natural history of gender diversity presenting in childhood and to investigate long-term outcomes for those receiving interventions. Methods and analysis Trans20 is a prospective cohort study based on children and adolescents first seen at the Royal Children's Hospital Gender Service (RCHGS) between February 2017 and February 2020. Current estimates indicate the final sample size will be approximately 600. Patients and their parents complete online questionnaires prior to the first appointment with RCHGS and regularly thereafter as part of routine clinical care. On discharge from RCHGS, patients are invited to continue undertaking questionnaires biennially. In this way, a naturally forming cohort study has been created. The primary outcomes include gender dysphoria, physical and mental health, schooling, family functioning and quality of life. Subgroup analyses based on factors such as gender identity, birth-assigned sex and treatment received will be performed using bivariate and multivariate modelling as appropriate, and relevant statistical methods will be applied for the repeated measures over time.