Comparative results on survival of human and animal eggs using different cryoprotectants and freeze-thawing regimens. II. Human.

A total of 269 human pronuclear embryos and 84 oocytes were subjected to four different protocols of cryoprotectant equilibration, washing out and freeze-thawing. The morphological survival, rate of development, fertilization in vitro and overall survival rate were estimated in the groups of fresh, aged oocytes, diploid and multipronuclear embryos used. With some restrictions, the conclusion can be drawn that slow, low intermediary temperature 1,2-propanediol (1,2-PROH) and 1,2-PROH/dimethyl sulphoxide (DMSO) systems are superior to the rapid, high intermediary temperature 1,2-PROH and the traditionally used DMSO systems. The best success rates were reached with the combination of cryoprotectants in the low intermediary temperature group. Thirty-three patients had 37 transfers of cryopreserved pronuclear embryos (n = 103), resulting in eight pregnancies (24.2% per transfer) thus doubling the pregnancy rate in the stimulation cycles for the same period (21% per transfer). Thawing at a rate of 50 degrees C/min is not incompatible with the survival of slowly frozen human oocytes and pronuclear embryos cooled to an intermediary temperature of -70 degrees C using the DMSO system.