Comparison of spindle and chromosome configuration in in vitro- and in vivo-matured mouse oocytes after vitrification

Objective: To compare the cytogenetic changes in in vitro- and in vivo-matured oocytes after vitrification. Design: In vitro experiments using murine model. Setting: Animal model study in university laboratory. Animal(s): CD-1 mice. Intervention(s): In vitro maturation and vitrification of oocytes. Main Outcome Measure(s): Post-warming survival, analysis of spindle and chromosome configurations, aneuploidy screening of parthenogenetically activated oocytes, extent of DNA fragmentation, and early embryonic development after IVF. Result(s): Eighty percent of germinal vesicle-stage oocytes matured after in vitro maturation and were cryopre-served by vitrification (n = 354). There was no significant difference in the post-warming survival of in vitro- and in vivo-matured oocytes (94.1% vs. 91.8%, respectively). The majority of in vitro- and in vivo-matured oocytes maintained normal meiotic spindle morphology and chromosome alignment (88.2% vs. 86.9%, respectively) after vitrification and the incidence of aneuploidy was not increased (11.5% vs. 9.3%). However, in vitro-matured oocytes showed a higher rate of DNA fragmentation after vitrification compared to in vivo-matured oocytes. After vitrification, the cleavage and blastocyst formation rates of in vitro-matured oocytes were significantly lower than those of in vivo-matured oocytes (37.0% vs. 60.0% and 5.4% vs. 18.9%, respectively). Conclusion(s): Vitrification of in vitro-matured mouse oocytes results in high survival rates, normal meiotic spindle and chromosome alignment, and no increased incidence of aneuploidy. A possible cause of the reduced developmental competence of in vitro-matured and vitrified oocytes may be due to DNA fragmentation.