No funding was received for the conduct of this study. Members of the EndoKey study group did not receive payment. The authors and members of the EndoKey study group have no conflict of interest.

STUDY QUESTION What is the X chromosomal content of oocytes and granulosa cells of primordial/primary (small) follicles and stromal cells in ovaries of young patients with Turner’s syndrome (TS)? SUMMARY ANSWER Small ovarian follicles were detected in one-half of the patients studied, and X chromosome analysis revealed that most oocytes were normal, granulosa cells were largely monosomic, while stromal cells showed a high level of mosaicism. WHAT IS KNOWN ALREADY Most women with TS experience a premature reduction or complete loss of fertility due to an accelerated loss of gametes. To determine whether fertility preservation in this group of patients is feasible, there is a strong need for information on the X chromosomal content of ovarian follicular and stromal cells. STUDY DESIGN, SIZE, DURATION Small follicles (<50 μm) and stromal cells were isolated from ovarian tissue of young TS patients and analysed for their X chromosomal content. In addition to ovarian cells, several other cell types from the same patients were analysed. PARTICIPANTS/MATERIALS, SETTING, METHODS After unilateral ovariectomy, ovarian cortex tissue was obtained from 10 TS patients (aged 2–18 years) with numerical abnormalities of the X chromosome. Ovarian cortex fragments were prepared and cryopreserved. One fragment from each patient was thawed and enzymatically digested to obtain stromal cells and primordial/primary follicles. Stromal cells, granulosa cells and oocytes were analysed by FISH using an X chromosome-specific probe. Extra-ovarian cells (lymphocytes, buccal cells and urine cells) of the same patients were also analysed by FISH. Ovarian tissue used as control was obtained from individuals undergoing oophorectomy as part of their gender affirming surgery. MAIN RESULTS AND THE ROLE OF CHANCE Ovarian follicles were detected in 5 of the 10 patients studied. A method was developed to determine the X chromosomal content of meiosis I arrested oocytes from small follicles. This revealed that 42 of the 46 oocytes (91%) that were analysed had a normal X chromosomal content. Granulosa cells were largely 45,X but showed different levels of X chromosome mosaicism between patients and between follicles of the same patient. Despite the presence of a low percentage (10–45%) of 46,XX ovarian cortex stromal cells, normal macroscopic ovarian morphology was observed. The level of mosaicism in lymphocytes, buccal cells or urine-derived cells was not predictive for mosaicism in ovarian cells. LIMITATIONS, REASONS FOR CAUTION The results are based on a small number (n = 5) of TS patient samples but provide evidence that the majority of oocytes have a normal X chromosomal content and that follicles from the same patient can differ with respect to the level of mosaicism of their granulosa cells. The functional consequences of these observations require further investigation. WIDER IMPLICATIONS OF THE FINDINGS The results indicate that despite normal ovarian and follicular morphology, stromal cells and granulosa cells of small follicles in patients with TS may display a high level of mosaicism. Furthermore, the level of mosaicism in ovarian cells cannot be predicted from the analysis of extra-ovarian tissue. These findings should be considered by physicians when offering cryopreservation of ovarian tissue as an option for fertility preservation in young TS patients. STUDY FUNDING/COMPETING INTEREST(S) Unconditional funding was received from Merck B.V. The Netherlands (Number A16-1395) and the foundation ‘Radboud Oncologie Fonds’ (Number KUN 00007682). The authors have no conflicts of interest. TRIAL REGISTRATION NUMBER NCT03381300.

STUDY QUESTION What is the standpoint of an international expert panel on ovarian tissue cryopreservation (OTC) in young females with Turner syndrome (TS)? SUMMARY ANSWER The expert panel states that OTC should be offered to young females with TS, but under strict conditions only. WHAT IS KNOWN ALREADY OTC is already an option for preserving the fertility of young females at risk of iatrogenic primary ovarian insufficiency (POI). Offering OTC to females with a genetic cause of POI could be the next step. One of the most common genetic disorders related to POI is TS. Due to an early depletion of the ovarian reserve, most females with TS are confronted with infertility before reaching adulthood. However, before offering OTC as an experimental fertility preservation option to young females with TS, medical and ethical concerns need to be addressed. STUDY DESIGN, SIZE, DURATION A three-round ethical Delphi study was conducted to systematically discuss whether the expected benefits exceed the expected negative consequences of OTC in young females with TS. The aim was to reach group consensus and form an international standpoint based on selected key statements. The study took place between February and December 2018. PARTICIPANTS/MATERIALS, SETTING, METHODS Anonymous panel selection was based on expertise in TS, fertility preservation or medical ethics. A mixed panel of 12 gynaecologists, 13 (paediatric) endocrinologists, 10 medical ethicists and 20 patient representatives from 16 different countries gave consent to participate in this international Delphi study. In the first two rounds, experts were asked to rate and rank 38 statements regarding OTC in females with TS. Participants were offered the possibility to adjust their opinions after repetitive feedback. The selection of key statements was based on strict inclusion criteria. MAIN RESULTS AND THE ROLE OF CHANCE A total of 46 participants completed the first Delphi round (response rate 84%). Based on strict selection criteria, six key statements were selected, and 13 statements were discarded. The remaining 19 statements and two additional statements submitted by the expert panel were re-evaluated in the second round by 41 participants (response rate 75%). The analysis of the second survey resulted in the inclusion of two additional key statements. After the approval of these eight key statements, the majority of the expert panel (96%) believed that OTC should be offered to young females with TS, but in a safe and controlled research setting first, with proper counselling and informed consent procedures, before offering this procedure in routine care. The remaining participants (4%) did not object but did not respond despite several reminders. LIMITATIONS, REASONS FOR CAUTION The anonymous nature of this study may have led to lack of accountability. The selection of experts was based on their willingness to participate. The fact that not all panellists took part in all rounds may have resulted in selection bias. WIDER IMPLICATIONS OF THE FINDINGS This international standpoint is the first step in the global acceptance of OTC in females with TS. Future collaborative research with a focus on efficacy and safety and long-term follow-up is urgently needed. Furthermore, we recommend an international register for fertility preservation procedures in females with TS. STUDY FUNDING/COMPETING INTEREST(S) Unconditional funding (A16-1395) was received from Merck B.V., The Netherlands. The authors declare that they have no conflict of interest.

<b><i>Introduction:</i></b> Ovarian tissue cryopreservation (OTC) has proven to be effective in other patient groups, but the effectiveness in girls with Turner syndrome (TS) is still unclear. Guidelines for counselling about OTC in TS are lacking. The aim of this study was to gain insight into the experiences of patients, parents, and healthcare providers with the decision-making process regarding OTC in girls with TS. <b><i>Methods:</i></b> Within a year after counselling, a survey was sent to 132 girls with TS and their parents. Furthermore, focus groups were conducted with (1) gynaecologists with subspeciality reproductive medicine, (2) paediatric endocrinologists, (3) parents of girls aged 2–12, and (4) parents of girls aged 13–18. Transcripts were analysed using a thematic analysis approach. <b><i>Results:</i></b> The response rate of the survey was 45%. Of the survey respondents, 90% appreciated counselling regarding their future parenting options and considered it an addition to existing healthcare. Girls with TS and their parents indicated that the option of OTC raised hope for future genetic offspring and instantly made them feel that their only option was to seize this opportunity. Gynaecologists and paediatricians found it challenging to truly make families grasp a realistic perspective of OTC in girls with TS. <b><i>Discussion and Conclusion:</i></b> Offering young girls with TS the possibility of fertility preservation in an experimental setting raised high hopes and led to challenges for healthcare providers in ensuring a considered decision. The appropriate moment for counselling should be tailored to the individual and discussed with patient, parents, and paediatrician.