There are three main categories of factors that affect the fetal weight relationship: first, maternal factors, if the mother herself is short in stature, or multiple pregnancies, the mother’s nutritional status is poor. If the mother has chronic diseases, such as chronic hypertension, hypertension during pregnancy, diabetes combined with microangiopathy, severe congenital heart disease, and special medications used by the mother may lead to poor intrauterine growth and weight loss of the fetus. The second major factor is related to the placenta, which is the main provider of nutrition and nutrients for the child in utero, inflammation of the placenta itself, and chorioamnionitis. In addition, the single umbilical artery, i.e., only one umbilical artery, is more difficult to supply oxygen to the child, so the child will not grow well. The third major factor is related to the fetus itself, such as the child has chromosomal abnormalities, or congenital metabolic abnormalities, and some congenital intrauterine infections, these factors may cause the child’s growth and development is slow, weight does not grow up and other related conditions.