Vitrification of human 8-cell embryos, a modified protocol for better pregnancy rates.

Human day 3 embryos were vitrified in modified ethylene glycol-based protocol. The present study reports a post-thaw survival rate of 95.3%, which was significantly higher than that of the conventional slow-freezing protocol (60.0%, P < 0.05). The implantation and pregnancy rates were also higher (14.9% and 35.0%) than that in the slow-freezing protocol (4.2% and 17.4%). On average, three embryos were transferred per patient. Out of the 40 transfer cycles, five deliveries and nine ongoing pregnancies were achieved. Four ended with delivery of a singleton and one a miscarriage. Ethylene glycol is a good cryoprotectant to preserve human 8-cell embryos because of its low toxicity as shown by the high survival rate, and vitrification is a promising alternate to the conventional slow-freezing method.