Effect of Choline-supplemented Sodium-depleted Slow Freezing Versus Vitrification on Mouse Oocyte Meiotic Spindles and Chromosome Abnormalities

Objective: To evaluate and compare vitrification and choline-supplemented sodium-depleted slow freezing of mouse oocytes.

Design: Animal study.

Setting: University-affiliated hospital.

Animal(s): CD-1 mice.

Intervention(s): Oocyte cryopreservation by vitrification or choline-supplemented sodium-depleted slow freezing.

Main Outcome Measure(s): Survival rate, fertilization and embryonic development in vitro, meiotic spindle and chromosome configuration, and aneuploidy screening after parthenogenetic activation.

Result(s): A total of 564 oocytes were vitrified, and 791 oocytes were cryopreserved using the slow freezing. The survival rates were 91.8% (518/564) and 73.3% (579/791), respectively. After IVF, the cleavage and blastocyst formation rates of vitrified oocytes were significantly higher than those of slow-frozen oocytes (63.6% vs. 39.9% and 30.50% vs. 20.2%, respectively). Vitrified oocytes were more likely than slow-frozen oocytes to maintain normal meiotic spindles and chromosome alignment (86.9% vs. 70.1%). However, the incidence of aneuploidy was similar in vitrified oocytes and slow-frozen oocytes (9.30% vs. 8.7%).

Conclusion(s): Vitrification is superior to choline-supplemented sodium-depleted slow freezing, leading to improved survival, fertilization, and embryonic development in vitro. Analysis of meiotic spindle integrity and chromosome alignment indicates that less damage was detected in vitrified oocytes. However, the incidence of aneuploidy is similar in both vitrified and slow-frozen oocytes.