Many transgender and gender diverse individuals wish to undergo genital gender surgery as part of their gender affirming treatment. A variety of procedures and techniques for genital surgery are currently available. Options for feminizing surgery surgical are: vaginoplasty, vulvoplasty, labiaplasty, and clitoroplasty. For masculinizing genital gender surgery options are: phalloplasty, metoidioplasty, scrotoplasty and coronaplasty. For each of these procedures, several different surgical techniques are used.

Clinical research is important because it provides evidence on the benefits, effectiveness, and safety of the various surgical treatments. This knowledge is vital to be able to select the best treatment option for each individual.

It is increasingly recognised that involvement of the population concerned is essential. Otherwise, studies may not evaluate what really matters to the population.

Current research in the field of gender surgery is mostly about the safety and “success” of one specific surgical procedure, where “success” is defined in various ways. For instance, studies may report on sexual aspects or aesthetic outcomes. Also, when studies report on safety, diverse outcomes are measured. Presently, no consensus exists on the definitions of outcomes or on which measurement instruments should be used. This hinders comparison between studies and the advancement of knowledge.

To be able to compare procedures or techniques, outcomes measured in different studies should be comparable; which a COS can aid.

A Core Outcome Set is a standardized limited list of the most important outcomes that researchers should measure and report in all clinical studies concerning – in this case – genital gender surgery. The outcomes lists for feminizing and masculinizing genital surgery will naturally be different. They will be developed by the same methods but with different stakeholders. The outcomes must be relevant to the population, and there must be consensus about the definitions and the way they are measured.

When all researchers at the very least report on these standardized and most important outcomes, measured in the same way, we can compare and combine outcomes of different clinical studies and draw meaningful conclusions. Off course, researchers can always include extra outcomes in their studies. When research can be combined and compared, the quality of scientific evidence backing up guidelines and shared decision making, improves.

The GenderCOS project will develop two Core Outcome Sets:

1) A COS for feminizing genital gender surgery;

2) A COS for masculinizing genital gender surgery.

Development of a COS has three stages. In all stages participation of the transgender and gender diverse community and healthcare professionals is essential.

1. All possible outcomes are collected from clinical research and from interviews and focus groups with transgender and gender diverse people. A list of possible outcomes is drawn.

2. Experts by lived experience and professionals in the field of genital surgery form all over the world are invited to prioritize the outcomes in multiple rounds. Through analyses of the input the list is shortened over each round.

3. Consensus about the COS is reached through a consensus meeting in which all stakeholders are represented.

Participating involves completing all three rounds of Delphi surveys. The surveys are carried out with an interval of 2-4 months. After completing the last survey you can indicate if you are willing to act as a representative during the consensus meeting. When there are more volunteers then available spots, not all volunteers are invited to the consensus meeting.

Experts by experience:

• transgender- and/or gender diverse individuals who have undergone genital gender surgery at least 3 months previously, can read and understand English, and are of legal age to undergo surgery in country of received surgery.

Experts by profession:

• surgeons who are specialized in genital gender surgery (plastic surgeons, general surgeons, urologist, gynaecologists). Professionals in gender healthcare related to gender surgery (such as psychologists, physiotherapists, sexologists, physician assistants, nurses, psychiatrists). Authors who have published at least 5 articles on research into genital gender surgery and also have worked in gender care, treating transgender and gender divers individuals who have undergone genital gender surgery.

Participation is on a voluntary basis. We offer all participants the option to be named in the acknowledgements of the main publication on either Core Outcome Set. It is also possible to participate but not be named as a contributor.

As this project is not funded, there is no financial compensation for participation.

The results of the completed surveys will be encrypted and processed confidentially. Data will be stored on a secured drive of the Amsterdam UMC for a maximum of five years. This study was registered with the medical ethical board of the Amsterdam UMC, location VUmc under registration no. 2022.0102. It is always possible to quit participation during the study, email us at info@gendercos.org if you want to stop.