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:
Download OMI checklist here:
Inclusivity
and
Terminology
At GenderCOS, we care about using inclusive and respectful language. We try to use the most inclusive terminology possible, though we sometimes rely on umbrella terms for readability.
"Transgender" and "gender diverse" describe people whose gender identity and/or expression differs from their sex assigned at birth — including trans, nonbinary, gender nonconforming, agender, and other non-cisgender identities. Our work is meant to include everyone, regardless of how they identify.
In GenderCOS, “feminizing” surgery also includes de-masculinizing procedures, and “masculinizing” surgery also includes de-feminizing procedures. These terms describe types of surgical interventions and do not imply anything about a person’s gender identity. Our first two core outcome sets focus on these two categories to keep the scope manageable. We know other procedures exist and may require separate core outcome sets in future editions.
Questions or suggestions on how to make our work more inclusive? Please reach out 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.