The depth of amniotic fluid in the 3rd month of pregnancy is normal between 3-5cm. The depth of amniotic fluid is a dynamic process. Since fetal amniotic fluid is the external environment for fetal development during pregnancy, the amount of amniotic fluid is one of the very important reference standards for determining the condition of the fetus in the uterus. Doctors can assess the amount of amniotic fluid in the uterus by measuring the maximum depth of amniotic fluid. Excessive amniotic fluid causes over-distension of the uterus, which increases obstetric complications such as respiratory distress in the mother, preterm labor, premature rupture of membranes; for the fetus, it not only increases the risk of cesarean section and macrosomia, but also increases the risk of hereditary disorders, neurological abnormalities and other diseases after birth. When amniotic fluid is low in early pregnancy, the fetal membranes may adhere to the fetus, resulting in fetal malformations; if it occurs in the middle or late pregnancy, the pressure around the uterus acts directly on the fetus, which can easily cause musculoskeletal malformations; at the same time, amniotic fluid is prone to fetal distress and neonatal asphyxia. Pregnant women should undergo regular checkups so that problems can be detected at an early stage and timely measures can be taken.