Today, embryo freezing has become a fundamental part of every clinic's IVF programme, particularly when the emphasis is on singleton pregnancies. And the surest way to guarantee a singleton pregnancy is with the transfer of a single embryo in the treatment cycle. Single (or even two) embryo transfer, however, will mean that in many cases there are spare good quality embryos, and these can be frozen for later use - either to repeat the transfer cycle if the first does not succeed, or to be used for another baby if the first is successful.
With modern freezing techniques and greater experience, results from the transfer of frozen/thawed embryos are now almost as good as those with fresh embryos, so a store of embryos in deep-freeze can significantly add to the cumulative likelihood of pregnancy.
At the LWC good quality embryos are frozen after two or five days of development. They are frozen at an extremely low temperature (-196oC) using the vitrification method of very rapid freezing.