Comparison between slow freezing and vitrification of ovarian tissue cryopreservation in assigned female at birth transgender people receiving testosterone therapy: data on histological and viability parameters.

PURPOSE: The use of fertility preservation (FP) techniques has significantly increased in recent years in the assigned female at birth (AFAB) transgender population. Oocyte cryopreservation is the established method for FP, but ovarian tissue cryopreservation may be considered an alternative option, especially during gender-affirming surgery (GAS). The slow freezing (SF) cryopreservation technique is the standard method for human ovarian tissue, but recently, several studies have shown good results with the vitrification (VT) technique. The objective of this study was to compare the effectiveness of VT and SF techniques in ovarian tissue from AFAB transgender people. METHODS: This was a prospective study including 18 AFAB transgender people after GAS. Ovarian tissue pieces from each ovary were cryopreserved by SF and VT and compared with fresh tissue. Study by light microscopy (LM) assessed follicular morphology and density. The percentage of surviving and degenerated follicles was studied with the tissue viability test. Oocytes, granulosa cells and stroma were analysed separately by transmission electron microscopy. RESULTS: The VT technique preserves follicle and stromal tissue as well as the SF method, but with some differences. Evaluation by LM showed better follicle preservation with VT, but the ultrastructural study showed the presence of minor damage with both techniques compared to fresh tissue. CONCLUSION: Both cryopreservation techniques are accurate for maintaining the follicular population and stromal tissue. Further studies are needed to determine the impact of VT on ovarian tissue and the subsequent follicular activation mechanisms in AFAB ovarian tissue.