The World Egg Bank has used a slow freezing process since 2004 for egg freezing and thawing. 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 freezing.
Vitrification is a very rapid way of freezing eggs, which helps avoid damage during the freezing and thawing process. 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 freeze all of our donor eggs since the summer of 2008. The thaw rate for vitrification is generally between 80 and 90% with a fertilization rate between 70 – 80%.