Fetal macrosomia is a condition in which a baby is atypically large before birth. Macrosomia can be difficult to diagnose while the baby is still in the womb, but can be diagnosed as soon as the baby is born. Babies with macrosomia are born weighing more than 8 pounds and 13 ounces. The average newborn is about 7 pounds. Common causes of fetal macrosomia include genetics, obesity or diabetes in the mother. Sometimes, fetal macrosomia can make vaginal birth difficult, so a doctor may recommend a cesarean section (C-section) to avoid complications. Babies born with macrosomia are more likely to have low blood sugar, but most babies born with macrosomia will develop normally if they keep to a healthy diet with proper nutrition.