Fetal growth is a complex process influenced both by genetic (maternal and fetal) and environmental factors. It is important to understand both environmental and genetic determinants of fetal growth (a) for more effective clinical management of pregnancies and (b) because there are well documented associations between lower birth weight and a higher risk of chronic adult diseases, including cardiovascular disease, type 2 diabetes and hypertension (Barker et aI., 1993; Jarvelin et aI., 2004). The mechanisms underlying these associations are unclear. A clear understanding of the genetic contribution to fetal growth and its links with adult disease is important to inform our understanding of disease processes and thereby allow effective strategies for intervention and prevention.