The effects of freezing and 1, 2-propanediol on early and late pronucleate stage mouse ova were investigated in terms of survival after thawing and development in vitro. The samples were divided into two groups according to different age in
pronucleate
ova: ova in (1) early pronuclear stage with two distant pronuclei at 18h after hCG injection, and (2) late pronuclear stage with adjacent pronuclei at 30h. Zygotes in the late pronuclear stage have been proven to be more resistant to 1,
2-propanediol,
showing a significantly higher developmental rate than zygotes in early stage (80.3 versus 66.3%, P<0.05), but survival rate was similar in the two groups (91.0 versus 93.5%). After freezing and thawing, survival and developmental rates were
decreased
in both groups when compared to the control group (54.3 versus 92.3%, 47.7 versus 73.3%, respectively). And developmental rate in the late pronuclear stage zygotes showed significantly higher than in early (55.4 versus 40.0%) after thawing.
In conclusion, early pronucleate mouse ova have a lower developmental capacity in vitro and a lower survival rate after freezing and thawing than late ova. These findings suggest that the timing of freezing could be important for survival and
further
development in vitro in cryopreservation of human pronucleate ova.
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