Cryopreservation of embryos is the process of preserving an embryos at sub zero temperature. Since most IVF programs superovulate patients to grow many eggs there are often many embryos since the risk of multiple pregnancies increases with the number of embryos transferred many patients are left with spare embryos. It is now possible to freeze these embryos and store them in liquid nitrogen. These stored embryos can then be used later for the same patients so that she can have another embryos transfer cycle done without having to go through superovulation and egg collecting all over again. Freezing is very cost effective since transferring frozen thawed embryos is much less expensive than starting a new cycle.