Cryopreservation is a method used in medical biology that allows preserving the vitality of herbal, animal and also human cells by freezing them with liquid nitrogen.

The first cryopreservation of sperm was accomplished in 1949. Four years later the first pregnancy by the use of a deep frozen sperm was induced. In 1984, the first healthy child evolved from a cryopreserved embryo was born. Today cryopreservation is routinely used in reproductive medicine in order to increase the success rate of the IVF treatments while reducing the physical stress for the women involved. Imprinting and preserving surplus impregnated human female germ cells allows performing multiple fertilization attempts without necessitating the extraction of new oocytes in each cycle. In 2009, approximately 18.000 impregnated oocytes have been cryopreserved in German fertility clinics.

According to German jurisdiction it is allowed to cryopreserve impregnated germ cells for an indefinite period of time, the same applies to the cryopreservation of sperms. The cryopreservation of embryos and pre-embryos, however, is permitted in exceptional cases only (see: Embryo Protection Act, ESchG).

Possible negative side effects of cryopreservation (e.g. birth defects) have not been fully assessed yet. Considering that more than a thousand healthy children are born by IVF using cryopreserved impregnated germ cells in Germany alone each year, risks are usually classified as low. Critics of the method point out, that it is ethically problematic to impregnate and preserve more oocytes than can be transferred within one IVF cycle. Questions regarding the destiny of “supernumerary” embryos, particularly whether or not they may be used for research purposes, are at least partly due to the availability of the cryopreservation technique. Another matter of controversy is who is entitled to decide about the use or manipulation of the cryopreserved impregnated germ cells if gamete donors disagree, have separated from each other or deceased.