The vast majority of amniotic fluid is formed by fetal urine, which fills the amniotic cavity and enables the fetus to move freely in the uterine cavity, preventing limb adhesions of the fetus from occurring as limb malformations. In late pregnancy, amniotic fluid can promote fetal lung development, lubricate the birth canal, and facilitate smooth delivery of the fetus.1. Protect the fetus: amniotic fluid can enable the fetus to metabolize, grow and develop at a constant temperature, and can also expand the uterus to provide the fetus with an appropriate range of motion, allowing the fetus to do breathing exercises and limb activities in the uterus, helping the fetus to develop, preventing fetal limb adhesions, deformities or joint fixation, and protecting The skin of the fetal limbs is not damaged. Amniotic fluid can also isolate the fetus from the external environment to avoid infection; 2, maintain the balance of body fluids: the fetus can excrete urine into the amniotic fluid as a way to maintain the balance of its own body fluids; 3, promote lung development: in late pregnancy, because the amniotic fluid contains fetal alveolar surface active substances, more conducive to fetal lung development; 4, buffer external pressure: when the mother is subject to external impact or extrusion, it can play a 5, lubricating the birth canal: when the uterus begins to contract during labor, the pressure in the uterine cavity is transmitted from the amniotic fluid to the cervix to dilate the cervical opening and vagina, the amniotic fluid can avoid direct pressure on the maternal tissue from the fetal head, causing damage to the maternal soft tissue, and can also play a role in lubricating the birth canal.