Objective: To examine the ultrastructure changes and the effects of different sucrose concentrations on the developmental potential of human frozen-thawed oocytes at different maturity stages.
Methods: Oocytes at different maturity stages collected from polycystic ovarian syndrome patients were involved in the study. Different sucrose concentrations (0.1, 0.2 or 0.3 mol/L) were used to study the developmental potential of the frozen-thawed oocytes. Non-frozen and frozen-thawed different maturity oocytes were processed for transmission electron microscopy observation.
Results: The results revealed that the mitochondria and the vesicles in the immature oocytes cytoplasm were fewer than those in the mature oocytes without regular distribution. Electron density of the mitochondria and distribution of the vesicles in the mature oocytes changed with the cryopreservation. No remarkable change was produced in the immature oocytes between non-frozen and frozen-thawed oocytes. Cryopreserving with 0.2 mol/L sucrose resulted in perfect development potential for both mature and immature oocytes than that with 0.1 mol/L. Study involving 0.3 mol/L sucrose in the cryoprotectant resulted in higher survival rate and clinical pregnancies.
Conclusion: The results suggest that sucrose concentration of 0.3 mol/L in the cryoprotectant solution is efficient in freezing oocytes with slow-freezing method. Cryopreservation with slow-freezing method could produce ultrastructure changes in the human oocytes.