Morphological and apoptotic comparison of primordial and primary follicles in cryopreserved human ovarian tissue.

There are few reports which were designed to compare the survival rate of human primary follicles with primordial follicles after cryopreservation. This study was designed to evaluate whether such a difference occurs. Human ovarian biopsies were cryopreserved using dimethylsulphoxide/sucrose as the cryoprotectants. Fresh and cryopreserved ovarian samples were evaluated for viability differences between the two types of follicles using the endpoints of histology, ultrastructure and DNA fragmentation. In comparison with fresh ovarian tissue (83.9%+/-10.0%), the percentage of morphologically normal primordial follicles was not significantly different in cryopreserved tissue (73.9%+/-17.2%). However, a lower percentage of primary follicles with normal morphology was seen in the cryopreserved group (43.3%+/-25.7% vs 74.8%+/-19.4% for the fresh group). Transmission electron microscopy revealed that the cryopreservation did not appear to affect the structural integrity of primordial follicles; however, varying ultrastructural damage to the cytoplasm was observed in the majority of the cryopreserved primary follicles. Using a DNA fragmentation assay, the percentage of apoptotic primordial and primary follicles in the unfrozen (26.3% and 20%) and frozen (23.3% and 25%) ovarian tissue was similar. A higher proportion of primary follicles, compared to primordial follicles, suffer histological damage after slow freezing.