People who develop coronary heart disease or type 2 diabetes are now known to have grown differently to other people during fetal life, infancy and early childhood. This recent discovery is leading to a new'developmental'model for disease causation [1]. Associations between low birthweight and coronary heart disease and type 2 diabetes have now been shown among men and women in Europe, North America and India [2-7]. The association between low weight gain in infancy and coronary heart disease, first shown in men in Hertfordshire, UK, has recently been confirmed in Helsinki [1, 8]. In this latter cohort comprising 8760 men and women whose childhood growth was recorded, those who later de-veloped coronary heart disease or type 2 diabetes were small at birth, remained small in infancy but had accelerated gain in weight and body mass index thereafter [7, 8]. Low birthweight has been shown to predict altered glucose tolerance, raised blood pres-sure and hypertension in studies around the world [9, 10]. There is now strong evidence that these associa-tions are not the result of confounding variables. The biological basis for these associations appears to be two phenomena, developmental plasticity and compensatory growth [11]. Like other living creatures in their early life, human beings are'plastic'and able to adapt to their environment. For many of the body's organs and systems there is a critical period when they are plastic and sensitive to the environment. Most critical periods occur in utero. They are followed by loss of plasticity and a fixed functional capacity. Developmental plasticity is defined as the phenomenon by which one genotype can give rise to a range of different physiological or morphological states in response to different environmental conditions during development. It enables the production of phenotypes that are better matched to their environment than would be possible if the same phenotype was produced in all environments. Experimentally in animals it is surprisingly easy to produce lifelong changes in the metabolism and blood pressure of a fetus by minor modifications to the diet of the mother before and during pregnancy [12].

The growth of human babies has to be constrained by the size of the mother, otherwise normal birth could not occur. Small women have small babies: in pregnancies after ovum donation they have small babies even if the woman donating the egg is large. Babies may be small because their growth is con-