Anyone who has attempted to culture embryos knows how sensitive they are to their environment. Embryos provide the most stringent assessment of water quality, reagent purity, gaseous environment and technologist skills. For at least 15 years the transfer of cultured cattle and sheep embryos to surrogate mothers has been known to lead to unexpectedly large numbers of larger than normal offspring, a phenomenon attributed to sub-optimal culture conditions prior to transfer. More recently, the manner in which genetically identical mouse embryos are cultured has been shown to influence a range of behaviors in the animals after they are born, indicating subtle differences in their development. Not surprisingly, therefore, the developmental potential of an embryo might also be influenced by the conditions it encounters within the reproductive tract of the mother.

Recently much attention has been paid to the possibility that chemicals, posing as natural hormones, can influence a pregnancy outcome and the ‘‘quality’’of offspring born. Endocrine-disrupting chemicals undoubtedly pose a health threat to all living creatures and their progeny. Perhaps of even greater significance to human health and well being and ultimately to medical costs is the realization that the relative quality and quantity of ‘‘normal’’constituents, such as fats, proteins and carbohydrates, of a mother’s diet can subtly influence the phenotype of her offspring through epigenetic changes imprinted in utero.