143 Use of fertility preservation among a cohort of transgirls in the Netherlands 8 INTRODUCTION Many transgender adolescents wish to undergo gender-affirming medical treatment (GAMT), which may initially consist of puberty suppression (PS) with gonadotropinreleasing hormone analogues (GnRHa), followed by gender-affirming hormones (GAH) and, in adulthood, gender-affirming surgery (Coleman et al., 2012; Hembree et al., 2017). Whereas the effects of GnRHa are reversible, long-term use of gender-affirming sex steroids may affect fertility, and if gonadectomy is performed, the transgender person will definitely be infertile (de Roo et al.,, 2016; Hembree et al., 2017; Olson, Forbes, & Belzer, 2011). Infertility may have a major impact on the lives of transgender minors. Previous studies showed that concerns about (future) fertility are associated with a significant reduction in quality of life (Carter et al., 2010; Trent et al., 2003; Wenzel et al., 2005). Research among adult transmen described significantly better self-perceived mental health status and vitality among those with children than those without children (Wierckx et al., 2012). This suggests that fertility preservation (FP) can influence quality of life in transgender adolescents. A previous study showed that most transgender adolescents wanted to have children in the future (Strang et al., 2018). Another study, however, pointed out that transgender minors more often state “never wanting to have children” than has been reported in cisgender persons (Nahata, Tishelman, Caltabellotta, & Quinn, 2017). A survey revealed that 62% of adult transmen wanted to have children, and about 38% would have considered FP if it had been available at the time (Wierckx et al., 2012). Fifty-one percent of adult transwomen would have considered sperm cryopreservation if it had been offered (de Sutter, Verschoor, Hotimsky, & Kira, 2002). Nowadays, the World Professional Association for Transgender Health and Endocrine Society recommend counselling regarding FP options before initiating treatment with GnRHa (Coleman et al., 2012; Hembree et al., 2017). However, two recent studies from the United States indicate that transgender minors rarely use FP (Chen, Simons, Johnson, Lockart, & Finlayson, 2017; Nahata et al., 2017). We aimed to investigate how many adolescents made use of FP in a Dutch cohort of transgirls who started treatment with GnRHa. In addition, we assessed if information about the risk of infertility had been given, if discussion of the option of FP was documented in the medical file, and what the given reason for declining FP was if the adolescent had not made use of FP. Furthermore, we explored what factors were associated with the use of FP.