The development ofpre-elongation (ruminants) and preimplantation (e.g. mouse and humans) embryos ex vivo has evolved over the past four decades into a reliable technology that is used as a research tool in developmental biology, as well as other embryo technologies, for application in infertility treatment, species conservation and selective breeding. It is clear from a variety of embryo culture studies that adaptive responses by embryos during culture can lead to significant alterations in subsequent developmental profiles, the mechanisms of which are not entirely clear but are unlikely to be limited to a single mechanism because this does not account for the variability seen in responses and the emerging list of specific cellular stressors that cause long-term deviations in fetal development. Epigenetic mechanisms, especially deviation of methylation patterns, and adaptation via causal pathways linking gene expression signalling with critical developmental time points, especially of placental development, are two candidates. Observational studies on post-transfer consequences must now be designed so that specific candidate pathways are followed to elucidate their role in perturbed development following transfer.