Evaluation of meiotic spindles in thawed oocytes after vitrification using polarized light microscopy

Objective To investigate the efficacy of the PolScope on imaging the spindle morphology in oocytes at the metaphase II stage before vitrification and after thawing. Design In vitro study. Setting University infertility clinic and academic research laboratory. Intervention(s) Oocytes at the metaphase II stage that were obtained from superovulating mice were vitrified and then thawed. Main outcome measure(s) Morphological features of the spindle in oocytes were evaluated by both the PolScope and immunofluorescent staining. Result(s) Using the PolScope, the morphological features of the spindle of intact thawed oocytes were undetected by 3 hours of thawing in only 25% of cases. Most of the spindle images were recognized during the first hour of observation. Additionally, the statistical analysis of agreement of spindle morphology by both the PolScope and fluorescent staining showed a weighted Kappa value of 0.70, indicating good agreement. Oocytes with good spindle morphology verified by the PolScope before vitrification had a higher survival rate of intact oocytes after thawing compared with those with poor or undetected spindle images. Conclusion(s) The morphological features of the spindle in oocytes evaluated by the PolScope before freezing and after thawing are significantly correlated with those assessed by immunofluorescent staining after fixation. With the assistance of the PolScope, thawed oocytes with good spindle morphology can be verified and selected for further manipulation without fixation and staining.