ESPE Abstracts

Background: Transgirls (female-identifying adolescents assigned male at birth) can be treated with GnRH (gonadotropin releasing hormone analogs) followed by the addition of estrogens.

Recently in a small cohort of 25 transgirls their average final height was reported to be +1.9 SDS (standard deviation score) calculated for adult Dutch females.

High dosage estrogens can be used to stimulate bone maturation, thereby reducing final height. There are no reports on the effect of this treatment on final height in transgirls.

We present 11 cases of adolescent transgirls treated with high dose estrogens. Data on various approaches – limited duration of GnRH monotherapy, dosage and duration of estrogen therapy- and its efficacy on finale height are described.

Case series: At the start of GnRHa therapy mean height was 169.2 (±6.4) cm and the mean target height 186.4 (±4.8) cm. During GnRHa monotherapy until the start of estrogen therapy the mean predicted final height increased from 189.4 (±4.2) cm to 191.0 (±4.4) cm. According to protocol estrogen therapy was started at 5 µg 17-beta estradiol/kg and increased with 5 µg/kg every 6 months. The high dosage estrogen scheme was either 6 mg 17-beta estradiol (case 2 to 11) or 200 µg ethinyl estradiol (EE) once daily (case 1). Height reduction was calculated by the difference between final height and the predicted final height. The mean predicted final height at start of estrogen therapy was 193.2 cm (+3.6 SDS for Dutch females), the mean final height was 188.9 cm (+2,9 SDS for adult Dutch females) which means an average final height reduction of 4,3 cm (- 0,7 SDS). In 10 of 11 cases, final height was reduced. In 6 of those 11 cases estrogen therapy were started prior to the age of 16 . In case number 8, estrogens were started initially in low dosage which led to an increase of predicted final height.

Conclusion: Final height reduction in transgirls using high dosage estrogens can be achieved. However, final height of these transgirls was still above the normal range of biological girls. Further height reduction is feasible but may require adjustment of protocol. First, estrogens should be started at an earlier age. Second, the dosage of growth inhibiting effect of 17 beta estradiol should be increased or alternatively the synthetic estrogens should be used. Awareness of an increased risk of venous thromboembolic events by using synthetic estrogens is required and should be explored further.