Vitrification of In vitro -matured Oocytes: Effects of Meiotic Spindle Morphology on Clinical Outcome

Abstract

Objective: The meiotic spindle controls chromosome movement and mediates various functions essential for fertilization and early postfertilization events. This study aimed to examine whether vitrification causes meiotic damage in vitro- matured metaphase II (MII) human oocytes, and whether the meiotic spindle morphology influences the subsequent developmental outcomes. Methods: The spindle characteristics of MII human oocytesin vitro matured were studied before and after vitrification using PolScope imaging and immunofluorescence staining. The developmental competence of oocytes was also examined. Results: A total of 419 human MII oocytes were obtained from 593 intracytoplasmic sperm injection cycles at our hospital. Of these oocytes, 54 were used for immunofluorescence staining, whereas the other oocytes were examined by PolScope imaging and classified into three groups according to the meiotic spindle morphology: (A) normal morphology, (B) weak refraction and short meiotic spindle, and (C) no detectable meiotic spindle. The three groups demonstrated statistically significant differences in terms of survival after vitrification. However, differences were not found in terms of oocyte chromosome structure and meiotic spindle morphology on immunofluorescence staining performed before and after vitrification. Oocyte survival, fertilization, and early embryonic development rates were significantly higher in Group A than in Groups B and C with or without vitrification. While vitrification had no effect on these metrics in Group A, Groups B and C demonstrated significantly lower fertilization and cleavage rates after vitrification/warming. Conclusions: Screening for normal meiotic spindle morphology and chromosome configuration before vitrification may increase the yield of healthy viable oocytes for various assisted reproductive technologies.