Comparison between Slow Freezing and Vitrification in Terms of Ovarian Tissue Viability in a Bovine Model.

Objective  To assess the viability of bovine ovarian tissue after cryopreservation through either slow freezing or vitrification, and to compare it to that of control tissue by performing morphological analyses. Methods  The study included 20 bovine ovarian cortex fragments that were divided into control, vitrification, and slow freezing groups. Each group consisted of four fragments of the same ovary, two fixed without cultivation, and two fixed with cultivation. Tissues were evaluated based on follicular morphology immediately after heating and after 7 days of culture, and compared with the control group. Results  A total of 240 fragments were analyzed, generating a sample of 1,344 follicles without cultivation and 552 with cultivation. When the non-cultivated samples were classified as non-atretic follicles, 572 were found in the control group, 289 in the vitrification group, and 373 in the slow freezing group, showing no significant differences. When classified as atretic, 46 follicles were found in the control group, 23 in the vitrification group, and 41 in the slow freezing group, also showing no statistical difference. In the post-culture sample, an evolution of the follicular stages could be observed. This finding was important to support that the follicles considered non-atretic in the non-cultivated group were actually viable in the morphological evaluation. Conclusion  With no differences between the protocols, vitrification was shown to be an advanced and alternative method for patients who will undergo treatments that carry the risk of ovarian failure, as the method is less expensive, faster, and more adaptable to laboratory routine.