Diabetes is the most common endocrine disorder worldwide, with complications that include the development of both macro- and micro-vascular disease that contribute significantly to patient morbidity and mortality. The severity of diabetic complications is amplified during pregnancy, resulting in a higher incidence of adverse pregnancy outcomes such as pre-eclampsia, placental insufficiency and stillbirth than in non-diabetics. Vascular dysfunction is thought to underlie many of these complications, with the greatest impact occurring at the level of the resistance vasculature, where alterations in vascular reactivity can significantly affect blood flow and tissue perfusion. It is likely that problems associated with diabetic pregnancies are related, in part, to abnormal vascular function, particularly dysfunction of the vascular endothelium.