Embryo transfer involves the insertion of fertilized early-stage embryos into the female reproductive system. The technique does not alter the genetic composition of the embryo which was determined at fertilization. Using embryo transfer, a genetically dissimilar offspring, including embryos from differing species, can be nurtured through embryonic development.

Developments in reproductive technology are occurring at a rapid rate in agricultural animal science as well as in human biology. In vitro fertilization, embryo culture, preservation of embryos by freezing (cryopreservation), and cloning technology yield embryos that are produced outside of the female reproductive system.

There would be no need for embryo transfer if mammalian embryos could be cultured to maturity in the laboratory. While cell culture in vitro has made remarkable advances, embryos can be sustained in culture for only a few days. Accordingly, their survival is dependent upon transfer to the hospitable and nurturing environment of...