Excessive amniotic fluid may indicate some degree of structural developmental abnormality in the fetus, and when there is increased amniotic fluid, approximately 5% of fetuses will have significant structural abnormalities. Amniotic fluid is produced mostly from fetal urine, which is produced in a dynamic balance while the fetus is in utero. If during this process the fetus can only urinate but cannot swallow, for example, if there is a digestive tract obstruction, i.e., abnormal development of the digestive tract, the amniotic fluid will increase. Therefore, in case of excessive amniotic fluid, it is important to first suspect fetal developmental abnormalities, the most common of which is digestive tract obstruction. In addition, abnormalities in the development of the fetal central nervous system should be considered. The most common ones are anencephaly and cerebrospinal bulge, which can also cause excessive amniotic fluid because the exposed cerebrospinal membranes can seep out a lot of fluid. Therefore, a detailed ultrasound screening for malformations is needed to rule out structural abnormalities in all aspects of the fetus in case of excessive amniotic fluid.