Osmotic behavior of in vitro produced bovine blastocysts in cryoprotectantsolutions as a potential predictive test of survival

The osmotic behavior of bovine blastocysts produced in vitro was filmed dur ing exposure to and dilution of cryoprotectant solutions used for vitrifica tion. The relationship between the changes in the diameter of embryos and t heir subsequent survival was assessed. Embryos collected on Day 6 and Day 7 postinsemination were exposed to 10% glycerol (GLY) far 5 min, 10% GLY + 2 0% ethylene glycol (EG) for 5 min, and 25% Gly + 25% EG for 30 s, before di lution in 0.85 M galactose and finally in embryo transfer freezing medium ( ETF). Embryos that had a higher probability of survival behaved as perfect osmometers, shrinking, reexpanding, or swelling according to an identical p attern, whereas embryos that deviated from this standard usually did not su rvive. The initial embryo diameter, duration of shrinkage and expansion in 10% glycerol, duration of reexpansion in ETF, and final embryo diameter wer e clearly predictive of the ability to hatch after culture bl vitro. On a g iven day postinsemination, larger blastocysts were more likely than smaller blastocysts to survive and hatch after exposure to cryoprotectants with or without vitrification. (C) 2000 Academic Press.