Preterm infants are newborns born before 37 weeks of gestational age. Most preterm infants have a birth weight of less than 2,500 grams. 1. Appearance: Most weigh less than 2,500 grams. Body length is less than 47 cm, and cry is light. The neck muscles are weak, the limbs have low muscle tone, and the skin is red and tender. There are many fetal hairs, soft ear shells, unclear areola, few plantar lines, male infants’ testicles are not descended or not fully descended, and female infants’ labia majora cannot cover labia minora. 2, breathing: the respiratory center is relatively more immature. Breathing is irregular and apnea often occurs. Apnea refers to the respiratory arrest time of 15-20 seconds. Or less than 15 seconds, but accompanied by a slowed heart rate (<100 beats/min) and the appearance of cyanosis. Premature infants have immature lungs with little surface active material and are susceptible to pulmonary hyaline membrane disease. Premature infants with a history of intrauterine distress are prone to aspiration pneumonia. 3. Digestion: weak swallowing reflex, prone to choking on milk and aspiration of milk. The gastric cardia sphincter is relaxed, with a small volume, and is prone to overflow. Premature babies are preferable to breastfeeding. However, protein needs to be increased in time. Premature infants are prone to necrotizing small intestinal infection, pay attention to the osmotic pressure of milk should not exceed 460 mmol / l. Physiological characteristics 1, premature infants immature respiratory center, irregular breathing, often pause phenomenon. If the pause time exceeds 20 seconds, the heart rate is less than 100 times/minute. And the appearance of blue face, is called "apnea". This type of preterm infant is usually monitored in the hospital, and in case of apnea, the skin is stimulated and oxygen is administered, and if necessary, medication is administered. Premature babies cared for at home should be given more stimulation to make them cry and reduce the chance of apnea. If apnea has already occurred, do not panic, just play the soles of the feet or cheeks to make them cry out. Premature babies with repeated apnea should be noticed and sent to hospital if necessary. 2. Premature babies have a weak swallowing reflex and are prone to choking and misabsorption of milk. Overflow of milk is also more frequent than in full-term infants. The digestive enzymes are insufficient and the digestive capacity is weak, but the amount of nutrition required for growth and development is relatively high, so it is especially important to arrange and regulate feeding in a reasonable way. Premature infants should be fed with breast milk or preterm formula, starting with small amounts and gradually increasing. For those who have obvious difficulty in swallowing, a gastric tube is needed. 3, premature infants are more immature in the development of the thermoregulatory center, the ability to regulate body temperature is very poor, susceptible to external environmental temperature, the incidence of sclerosis in winter and autumn is extremely high, so to strengthen insulation. 4, premature infants leave their mothers prematurely, the immune antibodies from the mother are insufficient, and they are more likely to have various infections than normal infants. In addition, the physiological jaundice of preterm infants is heavy and long-lasting, and blue light irradiation is mostly used in the hospital. If the jaundice is not very severe, preterm infants at home can get more sunlight.