Core Outcome Sets & measurement instruments for masculinizing and feminizing genital gender-affirming surgery
The Core Outcome Sets and Outcome Measurements instruments are available for use!
The GenderCOS projects developed Core Outcome Sets (COS) for feminizing and masculinizing gGAS. The final COS include 20 outcomes overall, including patient-reported outcomes, clinical outcomes and adverse events. These outcome sets were developed through systematic literature reviews, qualitative interviews with transgender and gender-diverse individuals, a multi-round Delphi study, and a consensus meeting. The Outcome Measurement Instruments (OMI) for 19 of 20 unique core outcomes were established through a consensus process among professional experts in gender-care.
Publications
Outcome measurement instruments of both COS
Angelini M, Roijer PJ, Vallinga MS et al. Outcome measurement instruments for the core outcome sets on genital gender-affirming surgery: the GenderCOS project. EClinicalMedicine. 2026 Apr 18;95:103907. 10.1016/j.eclinm.2026.103907.
Core Outcome Sets
Vallinga MS, Roijer PJ, Pidgeon TE et al. The core outcome set for studies on feminizing genital gender-affirming surgery: findings from the GenderCOS project. EClinicalMedicine. 2025 Jul 1;85:103323. 10.1016/j.eclinm.2025.103323
Roijer PJ, Vallinga MS, Pidgeon TE et al. A core outcome set for research on masculinizing genital gender-affirming surgery: international consensus results from the GenderCOS project. EClinicalMedicine. 2025 Jul 1;85:103325. 10.1016/j.eclinm.2025.103325.
Protocol
Roijer PJ, Vallinga MS, Pidgeon TE et al. The GenderCOS project: study protocol for the development of two international Core Outcome Sets for genital gender affirming surgery. Int J Transgend Health. 2023 Dec 15;26(1):78-87. 10.1080/26895269.2023.2288881.
Contact us
If you would like to find out more, please contact gendercos@amsterdamumc.nl
Final GenderCOS
Download the two full COS including definitions here: Full COS
Download OMI checklist here: GenderCOS OMI
Inclusivity
&
Terminology
The GenderCOS project is committed to inclusivity and respectful language. We use inclusive terminology whenever possible, but sometimes use umbrella terms for readability. “Transgender” and “gender diverse” refer broadly to people whose gender identity and/or expression differs from their sex assigned at birth, including but not limited to trans, nonbinary, gender nonconforming, and agender people.
In GenderCOS, “feminizing” genital gender-affirming surgery also includes de-masculinizing surgery, and “masculinizing” surgery also includes de-feminizing surgery. These terms describe types of surgical interventions and do not imply anything about a person’s gender identity.
The first two GenderCOS core outcome sets focus on genital feminization and masculinization to ensure specificity and feasibility. We recognize that other genital gender-affirming procedures exist and may require separate core outcome sets in future editions.
Questions or suggestions about inclusivity can be sent to gendercos@amsterdamumc.nl.
The GenderCOS project Team
To ensure that the Core Outcome Sets are representative and will be usefull worldwide, we have assembled an international team of experts. Our steering team is formed by junior researchers, professionals working in gender care and two population representatives.