Comparison of ethylene glycol, 1,2-propanediol and glycerol for cryopreservation of slow-cooled mouse zygotes, 4-cell embryos and blastocysts

The aim of the study was to analyse the toxicity, the osmolar and cryoprote ctive activity of ethylene glycol (ETG) in terms of survival rate (SR), cle avage rate (CR) and expanded blastocysts percentage (EBP) of mouse embryos. Early mouse embryos and blastocysts were slowly cooled with ETG, 1,2-propa nediol (PROH) or glycerol, and thawed. The Van t'Hoff curve for 1.5 mol/l E TG showed recovery of initial volume within 4 min. No differences were obse rved in CR and EBP of ETG-exposed compared with non-exposed mouse zygotes, The SR of zygotes frozen with PROH was significantly better than with ETG ( 92% and 60% respectively; P < 0.01), and a significantly better EBP was ach ieved for blastocysts frozen with glycerol compared with ETG (75% and 50% r espectively; P < 0.05). For 4-cell stage embryos, no differences were obser ved in SR and EBP between ETG and PROH, Higher EBP was observed for 4-cell stage embryos (53%) frozen with ETG compared with pronucleate stage (19%) a nd blastocysts (48%), Low toxicity, good SR and EBP were observed for mouse embryos frozen with ETG, the best results being obtained at the 4-cell sta ge. At other embryonic stages, PROH and glycerol respectively seemed to pro vide better results.