Amniotic fluid is renewed in circulation through the production of urine by the fetus as well as secretion by the alveoli and continuous absorption by the fetus through swallowing. Amniotic fluid is the fluid in the amniotic cavity, the main component of which is water, and is initially composed of maternal serum, and in the middle of the pregnancy participates in the formation of amniotic fluid through the discharge of urine by the fetus, and in the late stages of pregnancy the fetal lungs will begin to participate in the formation of amniotic fluid as well. Thus amniotic fluid is constantly being swallowed by the fetus, secreted by the fetal body surface, alveoli, and excreted in urine to renew the circulation. Amniotic fluid plays an important role in protecting the fetus from external pressure and shock, and too much or too little amniotic fluid can affect the growth and development of the fetus.