OBJECTIVETo examine the influence of cryoloop on the spindle and chromosome configurations of human oocytes cryopreserved in the germinal vesicle (GV) and metaphase II (M II) stages, as well as on the survival rate and potential for in vitro maturation (IVM).

METHODSGV oocytes were randomly assigned into a control group (matured in vitro into the M II stage), a GV cryopreserved group (cryopreserved in the GV stage and then matured in vitro), and an M II cryopreserved group (matured in vitro and cryopreserved in the M II stage). After cryopreservation and IVM, immunostaining of the tubulin and chromatin was performed followed by visualization using laser scanning confocal microscopy (LSCM).

RESULTSA significantly higher survival rate was observed in the GV cryopreserved group than in the M II , but the maturation rate showed no significant difference between the GV cryopreserved group and the control (P > 0.05). Compared with the control group, there was a statistically significant decrease in the rates of normal meiotic spindles and chromosomes in the GV cryopreserved group (P < 0.05). A significantly lower rate of normal spindles was noted in the M II cryopreserved group than in the control, but no statistical difference was shown in the rate of normal meiotic chromosomes between the two groups (P > 0.05).

CONCLUSIONCryopreservation by cryoloop has a damaging effect on the spindle and chromosome of human oocytes in the GV and M II stages.