Clinically applied procedures for human ovarian tissue cryopreservation result in different levels of efficacy and efficiency

Different protocols are being used worldwide for the cryopreservation of human ovarian tissue for fertility preservation purposes. The efficiency and efficacy of the majority of these protocols has not been extensively evaluated, possibly resulting in sub-optimally cryopreserved ovarian tissue. To address the impact of this issue, we assessed the effects of two clinically successful human ovarian tissue slow-freezing cryopreservation procedures on the quality of the cryopreserved tissue. To differentiate between cryopreservation ( C ) versus thawing ( T ) related effects, four combinations of these two (A and B) very different cryopreservation/thawing protocols (A C A T , A C B T , B C A T , B C B T ) were studied. Before and after cryopreservation and thawing, the percentage of living and morphologically normal follicles, as well as the overall tissue viability, was assessed. Our experiments revealed that the choice of the cryopreservation protocol noticeably affected the overall tissue viability and percentage of living follicles, with a higher viability after protocol B C when compared to A C . No statistically significant differences in tissue viability were observed between the two thawing protocols, but thawing protocol B T required considerably more human effort and materials than thawing protocol A T . Tissue morphology was best retained using the B C A T combination. Our results indicate that extensive and systematical evaluation of clinically used protocols is warranted.