Baby crying at 4-5 am may be related to tummy hunger, environmental factors, or may be caused by indigestion, vitamin D deficiency rickets and other reasons. 1. Tummy hunger: if the baby is in the period of breastfeeding, usually need to eat milk once every 3-4 hours, in the morning at 4:00 or 5:00 a.m. when the phenomenon of tummy hunger may occur, it will cause crying. 2. Environmental factors: If the baby’s sleep environment is too noisy, or the temperature is too high, too low, etc., may lead to the baby feel uncomfortable, which may cause crying at 4:00 or 5:00 in the morning. 3. indigestion: in the dinner if the baby ate too much food, or a large number of cold and indigestible food, easy to cause indigestion, resulting in abdominal distension, abdominal pain, because of the body uncomfortable may cause four or five a.m. crying. 4. Vitamin D deficiency rickets: the disease can lead to increased neural excitability of the child’s brain, resulting in the child sleeping at night, always waking up frequently, which may show four or five a.m. crying, can also be accompanied by excessive sweating, occipital baldness and other symptoms. Baby crying at 4:00 am, may also be for other reasons, parents should pay attention to find the cause in a timely manner, if necessary, need to take the child to the hospital as soon as possible.