This depends on the stage of your embryos (when they were frozen) and on how many embryos you wish to be transferred. If you have cleaved embryos (frozen on day two or day three) or blastocysts (frozen on day five or day six), then we will thaw your embryos until there are enough surviving to meet the required amount for transfer.
If your embryos were frozen at the pronucleate stage (frozen on day one), then we will continue to thaw them until we have double the number that you need for transfer. For example, if you want two embryos transferred, we will thaw embryos until we have four surviving. This is because this stage of embryo still has to divide and, hopefully, it will allow you to have two good-quality embryos available for transfer.
Not all embryos or blastocysts will survive the freezing and thawing procedure, however. Our current thawing survival rate is approximately 80%.