VITRIFICATION OF MATURE MOUSE OOCYTES IN DIMETHYLSULFOXIDE - IMPROVEDRESULTS FOLLOWING THE ADDITION OF POLYETHYLENE-GLYCOL BUT NOT DEXTRAN

Oocyte viability has been improved following vitrification when the ma cromolecule polyethylene glycol (PEG, MW 8,000) was added to a 6M dime thylsulphoxide solution (VSD+PEG). To determine whether this beneficia l effect was specific to PEG or was purely due to the presence of a ma cromolecule, PEG was replaced by an equal amount of a similar MW dextr an (VSD+DEX). Viability was assessed by IVF; rates of normality, ferti lisation, blastocyst development and the overall % development to blas tocyst are quoted as median (range). Cryopreservation in VSD+PEG (n=17 7) resulted in rates of normality 94% (72-100%), fertilisation 90% (74 -100%) and development to blastocyst 71% (52-100) that were not signif icantly different from untreated oocytes (n=254) 90% (71-96%), 96% (78 -100%) and 81% (67-100%) respectively. Cryopreservation in VSD+DEX (n= 227) resulted in significantly reduced rates of normality 38% (6-69%) and fertilisation 57% (11-96%). Although cryopreservation in VSD+PEG h as resulted in the highest rates of survival of mouse oocytes to date, cryopreservation in VSD+DEX failed to afford the same protection.