Cryopreservation of human and rabbit oocytes and one-cell embryos: a comparison of DMSO and propanediol

The aim of this study was to improve the cryopreservation ofhuman oocytes and pronuclear embryos. One-step and multiple-stepaddition of dimethyl sulphoxide (DMSO) and 1, 2-propanediol(PROH) and three different freezing protocols with intermediatetemperatures of –35, –70 and –110°C wereinvestigated. This work was performed using rabbit oocytes aswell as human oocytes and one-cell embryos from the routineIVF programme. Also, human polyploid pronucleate oocytes wereused in controlled prospective studies of morphological intactnessand development in vitro. Rabbit oocytes survived best (113/126)when PROH was added in one step and controlled freezing stoppedat –110°C. But the development was better (141/187)if DMSO was added in multiple steps and the oocytes were cooledto –70°C before being plunged into liquid nitrogen.The mode of addition of the cryoprotectant influenced developmentonly if slow freezing was stopped at –35°C (51 versus34%). Using PROH, the development after thawing was also betterif cooling was stopped at –35°C (51 versus 37%) andDMSO was superior to PROH when the oocytes were cooled slowlyto –110°C (66 versus 37%). In the human, significantlymore pronucleated than unfertilized oocytes developed afterfreezing (92 versus 50%). The best results were achieved withpronuclear embryos using 1.5 M PROH and cooling to –110°C,when 91.7% of the surviving oocytes developed further. Thisis a marked improvement of the development rate and comparableto embryo freezing