Almost 10 years ago, it was proposed that the packaging of all devices and supplies used by diabetic patients for routine care should carry this warning label: 'Poor control of diabetes may cause birth defects. See your physician before becoming pregnant'. The present article reviews the evidence supporting the hypothesis that in mouse and rat experimental models, maternal pre-conceptional diabetes induces severe developmental alterations in embryos before and at implantation. The review (i) summarizes observations on embryos exposed to maternal diabetes in utero, (ii) summarizes data obtained by culturing embryos in vitro in the presence of high concentrations of D-glucose, (iii) discusses the possibility that alterations in the release of cytokines and growth factors by uterine cells contribute to early embryopathy and (iv) summarizes the evidence that apoptosis, a process of normal embryonic development, may be disrupted in blastocysts exposed to diabetic conditions in vivo and in vitro