The relationship between assisted reproductive technologies (ART) and deregulation of genomic imprinting is thought to have particular relevance to fetal growth because fetal growth is suggested to be the main drive for the evolution of imprinting or the conflict between the parental genomes. The link between embryo culture and phenotype is thought to be, at least in part, epigenetic. Genomic imprinting is an important epigenetic mechanism through which some aspects of fetal growth and development are regulated. Imprinting is controlled by allelic methylation, and the setting up of imprints in the female germline is a process that occurs throughout reproductive life. Inappropriate methylation or expression of imprinted gene clusters cause a range of pathologies, often involving aberrant growth and development. Similarly, the use of ART has been shown to cause disorders of growth in humans and other mammals.