Undernutrition continues to be high in many regions of the developing world. Birthweight, a common proxy measure of intrauterine growth, is influenced by nutritional, environmental and lifestyle factors during pregnancy and, in turn, affects immediate survival and function, and is a determinant of later life risk of chronic diseases. Maternal pre-pregnancy weight and height are independently associated with birthweight and also modify the effects of pregnancy weight gain and interventions during pregnancy on birthweight and perinatal mortality. Other prenatal factors commonly known to impact birthweight include maternal age, parity, sex, and birth interval, whereas lifestyle factors such as physical activity and maternal stress, as well as environmental toxicants have variable influences. Tobacco and other substance use and infections, specifically ascending reproductive tract infections, malaria, and HIV, can cause intrauterine growth restriction (IUGR). Few studies have examined the contribution of prenatal factors including low birthweight to childhood wasting and stunting. Studies that have examined this, with adequate adjustment for confounders, have generally found odds ratios associated with low birthweight ranging between 2 and 5. Even fewer studies have examined birth length or maternal nutritional status as risk factors. More research is needed to determine the proportion of childhood under-nutrition attributable to IUGR so that interventions can be targeted to the appropriate life stages.