Many factors influence whether an infant will have a low, high or normal birth weight. A baby born at full term usually weighs between 6 and 9 pounds and measures between 19 and 21 inches. (The average weight of a newborn is 7 lbs. 8 oz.). It is important for an expectant mother to get prenatal care to monitor her baby's growth and take good care of herself to increase her chances of having a healthy baby.