The average weight of a newborn depends on many factors. Some of these factors include size of the parents, multiple births, birth order and gender. If the parents of the newborn are large, you can expect to find a larger newborn, both by weight and height. If the newborn is a multiple, each baby born after the first will likely weigh less. As for birth order, with each subsequent pregnancy the baby typically weighs more than the one before. Lastly, newborn boys tend to be slightly larger than newborn girls.WarningA newborn's birth weight also can depend on the mother's health during the pregnancy. If a mother was undernourished during her pregnancy, it is possible that the baby also was malnourished. Mothers who are diabetic or get gestational diabetes are monitored because of the potential to have newborns that are much larger than normal.