Macrosomia basically refers to when a child has an abnormally high birth weight (usually defined as >9 lb or 4 kg). It is usually due to one of the following three factors: the mother's obesity/excessive weight gain during pregnancy, the mother's gestational diabetes or, lastly, the mother had poorly controlled diabetes mellitus. See this causes the developing fetus to experience intermittent hyperglycaemia, which in turn stimulates the production of various hormones (like insulin, growth hormone, insulin-like growth factor, etc.) which stimulates fetal growth. Complciation so macrosomia for the infant include hypoglycaemia, blood cell or electrolyte abnormalities which can become life-threatening, etc.