Objective: To evaluate the development of immature oocytes after freezing-thawing by conventional cryopreservation method for mature oocytes.
Methods: Immature oocytes were collected from stimulated ovaries of intracytoplasmic sperm injection (ICSI) cycles. Immature oocytes were in vitro matured directly or after slow freezing-fast thawing and immunostained for tubulin and chromatin and at last visualized by confocal microscopy.
Results: No statistical difference was found in maturity rate between freezing groups and the controls. There was a statistically significant increase in abnormalities of chromosome (23.7% vs. 50%) and spindle (28.9% vs. 53.9%) in the GV freezing group compared with the GV control (P < 0.05). MI groups gave the same results. But we did not find any statistical difference between GV frozen group and MI frozen group.
Conclusions: Cryopreservation decreases the ability of immature oocytes to form normal meiosis spindle and induce abnormal division of chromosomes. This suggests that the routine slow freezing-fast thawing procedure for mature oocyte couldn't preserve the ability well to form normal meiosis spindle during in vitro maturation.