Fetal development in utero is the initial link and important stage of the whole physiological development process of human. It has the following characteristics: i. Growth rate: The linear growth rate of fetal length reaches its peak at 15 weeks of gestation, and such growth rate will not occur again after birth. Weight increment: The rate of fetal weight gain reaches its peak at 32-34 weeks of gestation. Third, organ development: During fetal growth, the development of various organ systems is unbalanced, with the muscles being slower and the nervous system being the fastest.