The average newborn weight is about 7 pounds 8 ounces (3,400grams). The term macrosomia is used to describe a newborn with an excessive birth weight, which literally means large body. The diagnosis of fetal macrosomia can be made only by measuring birth weight after delivery.t full term, the avarage baby will be about 20 inches (51 cm) long and will weigh approximately 6 to 9 pounds (2700 to 4000 grams). - During a normal pregnancy your baby will grow and develop at about the same rate as any other pregnancy.