Meiotic spindle size is a strong indicator of human oocyte quality

PURPOSE: To investigate the relationship between the meiotic spindle size in human metaphase II oocytes and embryo developmental potential after intracytoplasmic sperm injection (ICSI). METHODS: Analyzed were 1302 oocytes with a visible meiotic spindle from 281 patients aged under 40 years undergoing ICSI cycles. The meiotic spindle was imaged by using PolScope before ICSI. The oocytes were classified into three groups, according to spindle size: group A (<90 μm(2)), group B (90‐120 μm(2)), and group C (>120 μm(2)). RESULTS: Overall, 389 (29.9%) oocytes were classified into group A, 662 (50.8%) into group B, and 251 (19.3%) into group C. The fertilization rate of the group B oocytes was significantly higher than for the A and C oocytes. The blastocyst formation rate in group B was significantly higher than in group A. In addition, the pregnancy rate in group B was significantly higher than in the other two groups. CONCLUSION: The oocytes with a spindle size of 90‐120 μm(2) showed higher fertilization, blastocyst formation, and clinical pregnancy rates than those with larger or smaller spindles. The measurement of the meiotic spindle size thus has a positive predictive value for identifying human embryo developmental potential clinically.