The causes of low weight infants are as follows: 1. Premature birth is the most important cause of low weight infants, and prevention of preterm birth is the most important treatment measure to prevent low weight infants. Low weight infants are newborns weighing less than 2500g, mostly caused by prematurity; 2, maternal factors, such as short stature, malnutrition, and previous history of low birth weight infants, mothers with early pregnancy infections, eclampsia, hypertension, smoking, small placenta, uterine abnormalities and other factors; 3, fetal factors, such as twins, multiple births, and chromosomal disorders, can cause low weight babies.