Abstract and Introduction
Abstract
Context: Growth is an important topic for many transgender boys. However, few studies have investigated the impact of puberty suppression (PS) and gender-affirming hormone treatment (GAHT) on growth and adult height.
Objective: To evaluate the effect of PS and GAHT on growth and adult height.
Design: Retrospective cohort study.
Setting: Specialized gender identity clinic.
Participants: A total of 146 transgender boys treated with GnRH analogues and testosterone who reached adult height.
Main Outcome Measures: Growth, bone age (BA), adult height, and difference between adult height and predicted adult height (PAH) and midparental height.
Results: In those with BA ≤14 years at start (n = 61), a decrease in growth velocity and bone maturation during PS was followed by an increase during GAHT. Adult height was 172.0 ± 6.9 cm; height SD score was similar to baseline (0.1; 95% CI, −0.2 to 0.4). Adult height was 3.9 ± 6.0 cm above midparental height and 3.0 ± 3.6 cm above PAH at start of PS. A younger BA at start PS was associated with an adult height significantly further above PAH.
Conclusion: During PS, growth decelerated followed by an acceleration during GAHT. Although adult height SD score was similar to baseline, adult height was taller than predicted based on BA at baseline, especially in those who started treatment at a younger BA. It is reassuring that PS and GAHT do not have a negative impact on adult height in transgender boys and might even lead to a slightly taller adult height, especially in those who start at a younger age.
Introduction
Gender dysphoria involves an incongruence between the experienced gender and the sex assigned at birth.[1] Medical treatment for adolescents consists of puberty suppression (PS) and subsequent gender-affirming hormone treatment (GAHT). PS with GnRH analogues (GnRHa) inhibits the development of undesired secondary sex characteristics and gives adolescents more time to explore their gender identity. If the gender-dysphoric feelings persist during the puberty-suppressive phase, GAHT may be initiated from the age of approximately 16 years to induce development of secondary sex characteristics congruent with the affirmed gender.[1]
In transgender boys (female sex assigned at birth, male gender identity), GAHT consists of intramuscular or transdermal testosterone. This induces physical changes such as increased facial and body hair, increased muscle mass, and lowering of the voice. Growth and predicted adult height are also topics of interest during consultation. Because Dutch males reach a mean adult height 13.1 cm taller than Dutch females,[2] height is also considered a sex characteristic. When treatment is initiated before adult height has been reached, transgender boys may ask how treatment will impact their growth and whether they will reach an adult height within the male population range. However, although the impact of GnRHa and GAHT on growth in transgender girls has recently been evaluated,[3] the effect on growth in transgender boys is still unknown.
The limited data available in transgender boys solely describe the effects of GnRHa on growth. Several studies have observed a decrease in height SD score (SDS).[4–6] Furthermore, it remains unclear whether testosterone can induce catchup growth and reverse the changes in height SDS that occur during GnRHa treatment.
The timing of treatment initiation might also play a role in the effects on growth. It has been suggested that treatment with PS and GAHT might have a negative impact on adult height.[7] Therefore, some clinicians argue that postponing treatment with GnRHa until growth is (nearly) finished may result in a taller adult height. This poses a dilemma for young transgender boys between achieving maximal growth and preventing the development of unwanted secondary sex characteristics such as breast development. The latter may give great distress because of the need to wear binders for several years and the wish to undergo a mastectomy.[8]
Another hypothesis is that the effect of testosterone on growth is dose dependent. Rapid increase of the testosterone dose may cause rapid acceleration of bone maturation, thereby shortening the period of growth. This may compromise adult height. In contrast, a more gradual increase of testosterone dosage may induce an increase in growth rate during a longer period, leading to an increased adult height, which is why a different dose schedule is proposed for adolescents that have and have not finished linear growth.[1] However, the effects of different testosterone dose schedules on growth and adult height in transgender adolescents have not been studied.
With this cohort study, we aim to evaluate the effect of GnRHa and testosterone treatment on growth in transgender boys. Furthermore, the impact of timing of treatment, tempo of dose increase, and body mass index (BMI) will be investigated. We hypothesize that PS will result in a decrease of growth velocity and GAHT will result in subsequent catchup growth that may be greater when the testosterone dose is slowly increased. Additionally, we expect these effects to be larger in subjects with a younger bone age (BA) at the start of PS.
J Clin Endocrinol Metab. 2023;108(2):414-421. © 2023 Endocrine Society
