Infants weighing less than 2500g are called low birth weight infants, including premature infants, overdue infants with placental insufficiency at 42 weeks of gestational age, preterm infants or immature infants are those born alive at less than 37 weeks of gestational age, and less than gestational age infants are those whose birth weight is less than ten percent of the normal weight value for the same age. Premature infants are not mature due to insufficient gestation, immature function of various organs and weak living ability, and less than gestational age infants are often caused by chronic intrauterine hypoxia causing fetal malnutrition, growth disorders, affecting brain development, resulting in mental retardation, poor prognosis, high disability rate and high mortality. It adds a lot of extra burden to families and society. Therefore, understanding the causes of prematurity and pay attention to it, can effectively avoid the occurrence of low birth weight infants, to reduce mortality, disability rate is of great importance. Etiology 1, maternal factors less than 18 years of age, more than 40 years of age, excessive smoking, drug and alcohol abuse, weight less than 45kg, prone to preterm birth. High fever, endocrine disorders, reproductive organ abnormalities, malnutrition, hyperemesis, intrauterine infections, q hair membrane amnionitis, etc. The important pathogens causing intrauterine infections are rubella virus, cytomegalovirus, toxoplasma, herpes simplex, Chlamydia trachomatis, mycoplasma, anaerobic bacteria, etc. Pregnancy combined with acute and chronic diseases such as pyelonephritis, chronic nephritis, bacteriuria, anemia, diabetes, hypertension, hyperthyroidism, etc. can endanger the life of mother and child. 2. Placental factors: placenta praevia, premature rupture of placenta, abnormal fetal position. 3.Fetal factor: multiple fetuses, sagittal, intrauterine infection. 4.Trauma, fall and flash can cause premature birth. 5.Sudden mental stimulation such as anger can induce preterm labor. 6.Dry stool, expectant mothers have thirst and irritability, sores on the tongue, dry lips, dry stool for several days, resulting in abdominal pain and premature delivery. 7, the fear of cold abdominal pain can lead to premature delivery. 8, sexual intercourse can cause premature rupture of the fetal membranes and amniotic cavity infection, orgasm can induce uterine contractions, semen containing prostaglandins can cause uterine contractions leading to premature hemorrhage more than, now, many healthy pregnancies premature births occur more than due to this. Prevention All pregnant women should have regular prenatal checkups during pregnancy, and for those with high-risk factors, active interventions should be made. 1.Enhance nutrition can reduce premature rupture of membranes and preterm delivery. 2.Avoid overexertion and stumbling, appropriate bed rest, especially in the left side of the bed in late pregnancy, which can increase blood flow to the uterus and placenta and prevent and reduce spontaneous uterine contractions. 3.Avoid mental stimulation. 4.Avoid infection. 5.Quit smoking and alcohol detoxification. Avoid contact with cats, dogs, pigeons and other pets. 6, reduce sexual intercourse, especially in late pregnancy and a history of premature birth should be prohibited. Must tolerate desire and avoid intercourse, do not want to have a moment of pleasure, from the dangerous way, to lifelong regret, careful.