Swiss ProspectivE Cohort of TRAnsgender and gender diverse individuals – The SPECTRA Study

The transgender and gender diverse population represents a significant and growing demographic globally. In 2023, 6% of the Swiss population identified as non-binary, gender non-conforming, or gender fluid. Despite greater visibility, transgender people continue to experience health disparities and poorer outcomes, particularly those with non-binary identities. In German-speaking northern and central Switzerland, three gender clinics have coordinated to standardise care and provide the infrastructure for prospective research, which remains limited nationally. This project will establish Switzerland’s first prospective observational study in transgender medicine, generating essential data to inform clinical guidance for this underrepresented population. Through national and international collaboration, it seeks to improve individual outcomes and strengthen Switzerland’s contribution to transgender health research, supporting a more inclusive healthcare system.

Switzerland’s healthcare system is advanced, yet access to transgender care remains difficult, especially in rural areas. Clinicians in cantonal and university hospitals have begun to coordinate. Basel hosts the largest multidisciplinary transgender centre, and a similar centre operates at University Hospital Zurich; a gender clinic was also recently established at Cantonal Hospital Lucerne. These three centres in German-speaking northern and central Switzerland provide a platform to harmonise interdisciplinary care and to initiate prospective research, still scarce nationally. In endocrinology, no established Swiss groups currently study endocrine transition longitudinally. The World Professional Association for Transgender Health Standards of Care (8th version; WPATH SOC8) recommends adapting guidance to local contexts so care reflects regional social and cultural realities (11). Coordinated prospective transgender research is therefore urgently needed.

Survey-based studies estimate that 0.3–6% of the population is transgender (1). In a 2023 global survey, 6% identified as non-binary or gender-fluid (2), suggesting substantial numbers also in Switzerland. The International Classification of Diseases (11th revision; ICD-11) defines “gender incongruence” as a persistent mismatch between experienced gender and sex assigned at birth (4), which may cause distress (“gender dysphoria”) (5) and drive demand for medical care. Gender-affirming hormone therapy (GAHT) is the most common medical intervention in transgender people (6,7) and aims to align physical traits with gender identity, promote gender congruence, and alleviate dysphoria (8). GAHT has systemic effects, yet major evidence gaps remain (1,9,10), including in Switzerland. This limits providers’ ability to deliver empirically grounded care and contributes to poorer health outcomes than in cisgender people.

Aims: This first Swiss prospective study will (i) assess effects of gender-affirming hormone therapy (GAHT) on health outcomes in binary and non-binary transgender adults, focusing on patient-reported outcome measures (PROMs); (ii) build national infrastructure for a Swiss Transgender Longitudinal Cohort. Methods: Multicentre prospective observational study at University Hospitals Basel and Zurich, and Cantonal Hospital Lucerne. Adults starting GAHT are seen every 3 months in year 1, then annually. Primary outcome: gender congruence at 12 months measured with the Gender Congruence and Life Satisfaction Scale (GCLS), compared in binary vs non-binary participants; GCLS captures non-binary experiences. Secondary outcomes: identity dynamics and GAHT regimens, cardiometabolic risk behaviours, minority stress, and detransition (rates/reasons). Key methods: peer advisory board; identity assessed at each visit; follow-up data collected for participants who stop GAHT or detransition.

University Hospital Basel, University Hospital Zurich, Cantonal Hospital Lucerne Fachgruppe Trans Transgender Network Switzerland Peer Representative Advisory Board International Scientific Advisory Board

This project will yield real-world evidence, with emphasis on patient-reported outcomes, enabling tailored clinical guidelines to reduce health disparities and improve local quality of care. The study will evaluate lifestyle factors and cardiometabolic risk markers alongside psychosocial stressors, providing an integrated view of physical and mental well-being during GAHT. Nationally, the study will strengthen collaboration across Swiss institutions and research networks, establishing a foundation for future transgender health projects. Findings will inform healthcare providers, policymakers, and communities, supporting personalized, evidence-based care strategies and a more inclusive healthcare system. Dissemination via national and international conferences and peer-reviewed publications will contribute to the global discourse on transgender health while directly addressing local healthcare gaps.

We have established the clinical and research framework to conduct this study. In 2022, we founded the “Gender Variance Innovation Focus” in Basel, Switzerland's most comprehensive interdisciplinary centre for transgender care which integrates multiple medical specialties. We also founded the Swiss Working Group on Endocrine Transgender Care, endorsed by the Swiss Society of Endocrinology (SGED), which published national guidelines for transgender endocrine care, helping standardize care across Switzerland. Through this Working Group, which brings together endocrinologists from all major Swiss transgender centres, we created a collaborative research network that enables a multicentre study. We contribute to the European transgender health research community through active participation in the European Professional Association for Transgender Health. Moreover, this project builds on an existing retrospective transgender cohort at the University Hospital Basel.