To avoid multiple pregnancies, it is important to select a single high quality embryo for transfer. Observation of meiotic spindles in oocytes is one way of evaluating embryo developmental competence. The spindle is non-invasively visualized by polarized light microscopy. It is possible to perform ICSI more safely and with optimal timing during meiosis by visualizing the meiotic spindle just before ICSI. In some human studies, it has been reported that oocytes with a spindle show significantly higher fertilization, blastocyst formation and pregnancy rates. Recently, it has been reported that morphological spindle normality is related to the live birth rate. In mice, the areas of the spindles in aged oocytes (23 h after hCG injection) are larger than those in young oocytes (15 h after hCG injection), and the blastocyst formation rate of aged oocytes is lower than that of young oocytes. Addition of MG132, a ubiquitin-mediated proteasome proteolysis inhibitor, to the medium prevents the spindle from becoming large and increases the blastocyst developmental rate. Therefore, it is thought that the spindle configuration and chromosome arrangement reflect the physiological stage or quality of an oocyte. Spindle imaging provides a useful index for comprehensively assessing embryo quality.