Most transgender boys reach their predicted adult height after treatment with gonadotropin-releasing hormone analogues and testosterone therapy, according to data published in The Journal of Clinical Endocrinology & Metabolism.

Sabine E. Hannema

“Many transgender boys do not want to compromise their adult height,” Sabine E. Hannema, MD, PhD, a pediatric endocrinologist at Amsterdam UMC in the Netherlands, told Healio. “Worries about how the treatment might affect their height previously caused a dilemma for some. Should they delay the start of treatment until after they had finished their growth spurt? Then they would have to endure progressive breast development and menstrual bleeding. With the results of the study, we can now reassure them that treatment does not affect adult height.”

Hannema and colleagues conducted a retrospective cohort study of 146 transgender boys attending the gender identity clinic at Amsterdam UMC’s Vrije Universiteit site from 1972 to 2018. Participants started pubertal suppression before age 16 years, received testosterone and had reached age 18 years at the time of data collection. Participants with a bone age of 14 years or younger at the start of pubertal suppression or those who reached menarche 1 year before pubertal suppression were placed in a pubertal group (n = 61; mean age, 12.7 years). Those with a bone age older than 14 years or who reached menarche 1 year or longer before starting pubertal suppression were placed in a postpubertal group (n = 85; mean age, 15.1 years). Bone age was determined by evaluating X-rays of the left hand. Height and weight were measured every 3 to 6 months after the start of pubertal suppression, and height and BMI standard deviation scores were calculated. Midparental height was calculated using a formula that incorporated paternal and maternal height. Female prediction tables were used to determine predicted adult height.

Most exceed predicted adult height

Mean height in the pubertal group was 158.3 cm at baseline and increased to 166.9 cm at the start of gender-affirming hormone therapy. Those with a bone age older than 12 years at the start of pubertal suppression had a greater decrease in height standard deviation score than those with a bone age 12 years or younger (mean difference, –0.6; 95% CI, –0.8 to –0.4), but scores did not differ at the start of HT.

The pubertal group had an increase in height of 5 cm from the start of HT to adulthood with a mean adulthood height of 172 cm. Of the group, 74% had a height taller than the predicted adult height at the start of pubertal suppression. Adult height was 3.9 cm above midparental height and 3 cm above predicted adult height at the start of pubertal suppression. Adult height was similar to predicted adult height at the start of gender-affirming HT.

Younger bone age linked to greater adult height

The time to reach adult testosterone dose did not influence height standard deviation score or adult height. Each year of younger bone age at the start of pubertal suppression was associated with 1.2 cm of adult height above the predicted height. A similar finding was observed with each year of younger bone age at the start of gender-affirming HT.

“Although adult height was unaffected by gonadotropin-releasing hormone (GnRH) analogue and testosterone treatment, 36% of transgender boys had an adult height below –2 standard deviation score compared to the general male population,” Hannema said. “Many ask about treatment options to enhance their growth, so this is a clinical need that requires further research.”

Among the postpubertal group, height increased 2.5 cm to a mean of 169 cm from the start of pubertal suppression to adulthood. Height increased 1 cm or more in 82% of the group. The pubertal group was 3 cm taller than the postpubertal group, but the difference between adult height and midparental height was not different between the groups.

“The findings were not surprising in the sense that my clinical impression was that transgender boys reached a normal adult height,” Hannema said. “On the other hand, findings that in girls with early-normal puberty treatment with GnRH analogues after age 8 years did not have a positive effect and may even have a negative effect on adult height caused some worry. From previous studies in transgender boys, we knew that growth decelerated during GnRH analogue treatment, but whether testosterone treatment resulted in complete catch-up had not been systematically investigated. I am glad we now have these data so that we can use these when counseling transgender boys and their families.”

For more information:

Sabine E. Hannema, MD, PhD, can be reached at s.e.hannema@amsterdamumc.nl.

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