Birth weight is an important predictor of perinatal complications and long-term health outcomes of offspring. Fetal programming influenced by maternal obesity, overnutrition, and hyperglycemia has been proposed as the fuel overload hypothesis. Recent investigations related with fetal body composition have revealed that neonatal adiposity can be predicted by fetal fat mass, and that maternal insulin resistance and serum leptin level are indicators of fetal adiposity. Based on the current evidence, the origins of obesity can partly be traced back into the fetal life. Further clarification of the determinants of fetal fat mass may lead to the clinical interventions and treatment strategies for fetal growth and development. This effort potentially leads to the elucidation of pathological conditions related with long-term health outcomes and the primary prevention of childhood obesity and early onset metabolic syndrome.