Human assisted conception: a cautionary tale. Lessons from domestic animals.

A variety of embryo-based technologies used in farm animal reproduction, including embryo culture, nuclear transfer, embryo-somatic cell co-culture and asynchronous embryo transfer can lead to the production of large offspring; the so-called large calf/lamb syndrome. In some cases, abnormalities in the fetus and newborn are apparent. The nature of these associations is explored with emphasis on the biological differences between in-vivo- and in-vitro-produced embryos. A unifying framework and research programme aimed at explaining anomalies in early embryo development is then proposed in terms of the response of somatic cells and embryos to cellular stress. The review concludes with a caution against developments in assisted conception technologies, in man and domestic animals, being determined too much by the needs of commerce at the expense of research on the molecular, biochemical and physiological basis of early mammalian development.