142 Chapter 8 ABSTRACT Purpose: The primary aims of the study are to examine the rate of attempted fertility preservation (FP) among a Dutch cohort of transgirls who started treatment with gonadotropin-releasing hormone analogues (GnRHa) and the reasons why adolescents did or did not choose to attempt FP. Methods: The study was a single-centre retrospective review of medical records of 35 transgirls who started treatment with GnRHa between 2011 and 2017. Results: Ninety-one percent of adolescents were counselled on the option of FP. Thirtyeight percent of counselled adolescents attempted FP, and 75% of them were able to cryopreserve sperm suitable for intrauterine insemination (IUI) or intracytoplasmic sperm injection (ICSI). Younger and Caucasian transgirls were less likely to attempt FP. No specific reason for declining FP was known in 33% adolescents, 32% of adolescents were not able to produce a semen sample because of early puberty, 17% felt uncomfortable with masturbation, 17% did not want to have children, and 13% wanted to adopt. Conclusions: One third of adolescents attempted FP, which is much more than the percentage reported in previous studies from the United States. One third of the transgirls could not make use of FP because they were unable to produce a semen sample because of early pubertal stage. For these adolescents, alternatives need to be explored.