Cohort Studies in Transgender Care

The Amsterdam Cohort of Gender Dysphoria (ACOG) has followed people applying to the gender clinic at what was then VUmc, now Amsterdam UMC, since 1972.

Amsterdam Cohort

The Amsterdam Cohort of Gender Dysphoria (ACOG) has followed people applying to the gender clinic at what was then VUmc, now Amsterdam UMC, since 1972. It is one of the longest-running cohort studies in the world; findings have been published by Wiepjes and colleagues, among others.

ENIGI

The European Network for the Investigation of Gender Incongruence (ENIGI) is a collaboration between European gender clinics, including those in Amsterdam, Ghent, Hamburg and Oslo, that has prospectively collected data on hormone treatment and outcomes since 2010.

Swedish population studies

Sweden combines population registers with clinical data, making unique epidemiological studies possible, such as Dhejne 2011 and Bränström 2019. Such registry studies offer large sample sizes but often lack detail about the clinical context. A summary of Dhejne’s Swedish long-term study, including the mortality figures, is available at genderrisico.nl.

What the Amsterdam cohort showed

The 2018 publication by Wiepjes and colleagues describes 6,793 people who visited the Amsterdam gender clinic between 1972 and 2015. The number of applications increased sharply during that period. Of those whose gonads had been removed, fewer than one percent reported regret to the clinic. The authors themselves identify an important limitation: a large proportion of the treated group had been lost to follow-up, and regret only came to light an average of several years after treatment. What Wiepjes and colleagues found specifically about detransition is discussed at transethiek.nl. Later research from the same clinic showed that more than four in five referred young people began a medical pathway.

Finnish registry studies

Finland also links data from gender clinics to national registers. A 2024 study led by Riittakerttu Kaltiala followed young people who had been referred to a gender clinic between 1996 and 2019. Suicide was rare in this group. The difference compared with their peers largely disappeared when the researchers accounted for previous psychiatric treatment. More information is available under suicide risk among transgender young people.

Strengths and limitations

Cohort studies follow large groups over long periods and show what happens in practice. They cannot prove that a treatment caused an outcome because the treated group was not assembled through random allocation. Attrition is the second problem: people who no longer visit the clinic disappear from the figures. See also bias in gender research.

Missing data

The Cass Review sought to link data from approximately nine thousand former patients of the English youth clinic with data from adult clinics, to determine how they had fared later in life. Most adult clinics did not participate. This example shows that long-term data are missing not only because research is difficult, but also because institutions do not always make such data available.