Gender dysphoria (GD) is defined as a marked incongruence between a person’s gender identity and the gender assigned at birth accompanied by psychological distress [1]. It is also the term for the diagnostic classification according to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Not all people who experience feelings of GD might be diagnosed with DSM-5’s ‘Gender Dysphoria’, because it is likely that they do not all seek assessment and gender affirmative treatment. For this reason and given the lack of systematic epidemiological studies, it is difficult to establish the prevalence of GD. Most former studies on prevalence of GD were based only on the numbers of individuals who are being treated at a transgender clinic. The prevalence in these studies in birth-assigned males ranges from 0.0004 to 0.0352% and in birth-assigned females from 0.0003 to 0.0066% [2]. In recent studies based on self-reported gender identity and GD, higher rates are reported, specifically in adolescents and younger adults [3]. E.g., the Williams institute, a public policy research institute on sexual orientation and gender identity, reports a survey-based prevalence of 0.7% of US adolescents who identify a transgender [4]. Another recent high school sample study that was held amongst 135.760 adolescents under the age of 21 years showed that 0.6% identified as the opposite gender and 3.3% identified as non-binary [5].

While medical gender affirming treatment with hormones and surgeries has been an accepted treatment for adults with GD since the 1970s [6], more reluctance exists concerning medical interventions in adolescents with GD. Some argue that puberty suppression by means of GnRH analogues or affirming hormonal treatment should not be initiated before a person’s physical puberty development is complete, because gender identity still may change during this phase of life, so adolescents should not make decisions regarding this subject [7]. Another point of concern is the lack of data on the long-term physical outcome and the signs from animal models that puberty suppression influences the brain development [8, 9].

Despite these reluctances, the introduction of supposedly fully reversible puberty suppression since the beginning of this century, to provide transgender adolescents who enter puberty with time to explore their gender identity, has rapidly become an accepted and widely prescribed medical intervention for adolescents with GD in Northern America (USA and Canada), and in some countries in Europe and Australia/New-Zealand [10, 11]. Puberty suppression was first introduced as a part of affirming treatment at the Center of Expertise on Gender Dysphoria in Amsterdam in The Netherlands, and therefore, GD treatment that includes puberty suppression is sometimes referred to as the ‘Dutch Model’ [12].

Few evaluative studies of this approach have been performed. Two studies on the first 55 adolescents treated at the Amsterdam clinic showed that behavioural and emotional problems and depressive symptoms decreased, while general functioning improved significantly during puberty suppression [13]. After gender affirming hormonal treatment and surgery, GD was alleviated and psychological functioning further improved [14]. A study on 201 adolescents who attended the transgender clinic in London found that puberty suppression in addition to psychological support was more helpful than psychological support on itself [15].

These results are promising. However, the participants were all adolescents who were referred to transgender clinics before the remarkable recent increase in the number of adolescent referrals [16, 17]. It remains, therefore, unknown whether the positive outcomes of early medical intervention also apply to adolescents who are referred in more recent years. There are several reasons why one could hypothesize that early referrals may differ from more recent registered adolescents. Due to the increased awareness of GD, it could well be that adolescents are referred at a younger age in recent years. In addition, the experimental character of medical treatment may first have attracted the most well-functioning group of adolescents with above average intelligence from stable families with a higher educational background able enough to support their off-spring to ask for a treatment that was still considered controversial in early years. The current flow of referrals might include families that are less well functioning in these aspects. The same may count with regard to co-occurring psychological problems. Finally, present referrals may have less extreme and non-binary forms of GD; a diagnosis of GD could be less likely in present referrals and a smaller percentage would start with medical treatment compared to the early years.

So far, one study has examined whether adolescents (N = 203) who were referred to a gender clinic in recent years were different from those in initial reports [18]. In contrast to initial studies, it was found that more birth-assigned females than birth-assigned males applied. Like the earlier studies, high rates of mental health difficulties were reported. Comparisons within the short 2.5 year period (2014–2016) of the first and second half of the adolescents showed that the age at first visit declined somewhat, while the presence of mental health difficulties did not change. Therefore, this study showed some changes over time, but the time span of the study seems too short to actual identify trends. Furthermore, the demographic and the psychological characteristics of the adolescents that were measured were very limited. For example, regarding psychological functioning, they only included the chart-reported mental health history and the Beck Depression Inventory [19].

To gain more insight in the possible change of characteristics of transgender adolescents, we conducted the present study in a large Amsterdam transgender clinic sample (N = 1072). The aim of this study is to examine whether there are time trends in demographic, psychological, diagnostic, and treatment characteristics in adolescents referred between 2000 and 2016.