The World Egg Bank has used a slow freezing process since 2004 for egg cryopreservation. This method provided an overall egg survival rate post thaw of about 60%. While we have achieved pregnancies and deliveries using this method, we have recently converted to using vitrification for egg cryopreservation.
Vitrification is a more rapid way of cryopreserving eggs, and prevents damage during the cryopreservation process that results from ice formation. Studies have shown higher survival and pregnancy rates using this method. In donor egg cycles, two recent studies show the industry experience with vitrification of donor eggs yield pregnancy rates equivalent to fresh donor egg cycle pregnancy rates.
The World Egg Bank has been using vitrification to cryopreserve all of our donor eggs since the summer of 2008. The egg survival rate for vitrification is greater than 90% on average, and the fertilization rate is approximately 85%.