In Germany, one to two embryos are usually transferred back into the uterus. It is forbidden by law to put back more than three embryos. If more than two fertilised eggs are available, it is possible to freeze them (cryopreservation, from Greek: cold and Latin conservare = to preserve). These eggs are thawed in a later cycle and, once they have developed further, are placed back into the uterus.

If the woman does not become pregnant in the first treatment cycle, the fertilised eggs can be thawed and replaced in any cycle without further stimulation and egg retrieval. The cryotransfer procedure is similar to embryo transfer in a fresh cycle and takes place either after ovulation or after mild hormonal preparation of the uterine lining.

This method can also be useful for sperm if collection is difficult, chemotherapy or radiotherapy is planned or the partner will be absent for a longer period of time.