Cryopreservation means preserving in a frozen condition. If extra embryos are left after an IVF / ICSI procedure they, too, can be frozen. Freezing spare embryos allows multiple embryo transfers from a single egg collection and improves the chance of live birth. Freezing is very cost effective, since transferring frozen embryos is much less expensive than starting a new IVF treatment cycle.

Not all embryos are suitable for freezing. The embryos can be frozen at the pronucleate, early cleavage or blastocyst stage. Overall about 50% of frozen embryos survive the thawing process.