Slow weight gain in the first month of an infant’s life may be related to physiological factors, or may be caused by gastrointestinal dysfunction, gastrointestinal diseases, congenital diseases and other reasons. 1. Physiological factors: commonly found in breastfeeding infants, due to the mother’s milk is not enough, milk is thin, or the number of feedings is not enough to meet the infant’s growth and development of the nutrients needed, it may lead to the baby’s first month of slow weight gain. 2. Gastrointestinal dysfunction: Because the gastrointestinal system of small infants is still immature, if parents do not feed properly, it is easy to lead to gastrointestinal dysfunction, resulting in the gastrointestinal tract’s digestive and absorptive capacity deterioration, which may result in the baby’s first month of slow weight gain. 3. Gastrointestinal diseases: such as intestinal tuberculosis, intestinal obstruction, etc., can lead to frequent abdominal pain, diarrhea, resulting in poor digestion and absorption, which may cause the baby’s first month of slow weight gain. 4. congenital diseases: common in congenital heart disease, congenital megacolon, congenital intestinal malformations and other diseases, may lead to infant growth retardation, resulting in the first month of infant weight gain slow. Slow weight gain in the first month, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.