Cryopreservation of human embryos using ethylene glycol in controlled slow freezing.

BACKGROUND Ethylene glycol (EG) has been successfully used as a cryoprotectant for vitrification of mammalian formula embryos (including human embryos) due to its low formula weight and high permeation into cells compared with other cryoprotectants, including propylene glycol (PROH). This study was carried out to evaluate the permeation and toxicity of EG and to investigate the effects of its use in a slow-freezing protocol on post-thaw development of mouse embryos and on pregnancy outcome of frozen human embryos. METHODS Spare human embryos after embryo transfer were cryopreserved using 1.5 mol/l EG or PROH using a slow-freezing protocol which had been tested previously in mouse experiments. RESULTS The post-thaw survival rate of human embryos in the EG group (80.6%) was significantly higher than that in the PROH group (65.2%, P < 0.05). The implantation and clinical pregnancy rates of human embryos in the EG group (20.3 and 46.9%) were significantly higher than those in the PROH group (7.5 and 24.6%, P < 0.05). CONCLUSIONS Ethylene glycol may be a good substitute for PROH to cryopreserve human embryos using a slow-freezing protocol.