Small for gestational age (SGA), also known as intrauterine growth retardation (IUGR) or small for gestational age, refers to a newborn whose birth weight is lower than the10th percentile of the average weight of the same gestational age, or lower than the average weight of the same gestational age by two standard deviations. These newborns are not only at high risk in perinatal period, but also have a series of problems in school age and adulthood. Specifically, the perinatal mortality rate of SGA children is much higher than that of normal-weight newborns, and the risk of illness increases accordingly. At the same time, these children are prone to cognitive impairment and decline in learning ability when they grow up to school age. As adults, many of them will be two standard deviations lower than the adult height of the normal population.