[Preservation by deep freezing of oocytes and embryos]

Although cryopreservation experiments with mammalian embryos have been performed for more than 30 years, definite progress was only achieved in the seventies. Investigations with mouse embryos have mainly contributed to the establishment of cryopreservation procedures for livestock embryos. Today the freezing of sheep and cattle embryos is applied to practice, but still transfer results range about 10% to 15% below comparable results obtained from transfer with fresh embryos. Procedures for the cryopreservation of mammalian oocytes and subsequent in-vitro fertilization of frozen/thawed oocytes are just being developed. Until now, only in the mouse a reproducable method for this purpose has been found. Meanwhile children were born from human in-vitro fertilization programs after cryopreservation of oocytes as well as embryos, although the cryopreservation of human embryos is facing major ethical objections.