The weight of a newborn at birth is related to the mother’s physical fitness, living standards during pregnancy, health care level, and nutrient absorption. The normal weight range of a baby after birth is 2500g-4000g. If the baby weighs less than 2500g, it is called a low birth weight baby. It is mainly seen in premature infants who are born before 37 weeks of gestation. Some full-term infants may also be underweight due to delayed growth in the mother. If the child's weight is greater than or equal to 4000g, it is called macrosomia. Most of them are caused by the pregnant mother having diabetes or the pregnant mother overeating in the third trimester. Within one week after birth, due to insufficient fetal milk intake, loss of water, discharge of meconium, etc., there will generally be temporary weight loss, which is medically called physiological weight loss. Physiological weight loss reaches its lowest point about three to four days after birth. The range of decrease is 3%-9% of body weight. It will gradually rise later and should return to the birth weight by 7-10 days after birth. If the child's weight loss exceeds 10% of the birth weight, is accompanied by other abnormal symptoms, or does not return to the birth weight two weeks after birth, possible pathological factors should be considered and a doctor should be asked to check for confirmation. It is common and normal for newborns born at full term to gain weight by 1-1.5 kilograms by the time they reach the full moon. If the child's weight gain does not meet the target, the first thing to consider is the child's insufficient milk supply. It is best to confirm the milk supply as soon as possible, and if necessary, timely supplement milk or increase formula milk. If the child shows signs of discomfort or the child has gained very little weight, it is recommended that parents take the child to the neonatology department for examination. The doctor may conduct examinations to rule out whether the child has hypothyroidism or genetic metabolic diseases that are causing the child's poor growth and development. The above data are just averages. There are individual differences in baby's growth to a large extent. There is no need to blindly pursue the baby's weight gain. Pay special attention not to overfeeding. As long as the baby's weight growth is within a reasonable range.