The normal range of the amniotic fluid index at 38 weeks of pregnancy is 8-18 cm. if the amniotic fluid index is <8 cm, the amniotic fluid is considered to be low. when the amniotic fluid index is <5 cm, the diagnosis is that the amniotic fluid is too low. If the amniotic fluid index is >18cm, the amniotic fluid is considered to be excessive. If the amniotic fluid index is ≥25cm, the diagnosis of excessive amniotic fluid is clear. Under normal circumstances, the production and absorption of amniotic fluid are in dynamic balance. When there is an imbalance between the production and absorption of amniotic fluid, it can cause abnormal amniotic fluid volume. During the 38th week of pregnancy, the fetal size can be measured, the fetal weight can be assessed, and the index of amniotic fluid and the depth of amniotic fluid can be measured by doing fetal 3D ultrasound. If there is excessive amniotic fluid, first of all, we should pay attention to whether the fetus has developmental abnormalities. Excessive amniotic fluid is closely related to neurological and digestive tract abnormalities. Neurological abnormalities are commonly seen in anencephaly, spina bifida and other neural tube defects; digestive tract abnormalities are mainly esophageal and duodenal atresia, which may occur when the fetus cannot swallow amniotic fluid, resulting in amniotic fluid collection. In addition, if there are lesions of the placenta and umbilical cord, placental chorionic hemangioma >1cm in diameter may also cause excessive amniotic fluid. Low amniotic fluid is often caused by abnormalities in the fetal urinary system, or by hypoplasticity. Abnormal amniotic fluid volume not only indicates a possible fetal abnormality, but may also lead to fetal death. Active diagnosis and treatment is recommended, depending on the presence or absence of fetal structural abnormalities, the gestational week and the severity of maternal self-conscious symptoms.