The causes of excessive amniotic fluid are complex, and about 1/3 of them are unknown. Generally speaking obvious excess amniotic fluid may be related to fetal structural abnormalities, pregnancy complications, complications and other factors. The details are as follows: 1. Fetal diseases: abnormal fetal development, or fetal metabolic diseases, chromosomal diseases, genetic genes and other abnormalities, apparently too much amniotic fluid, usually accompanied by fetal structural abnormalities, with neurological and digestive system abnormalities being the most common. Neurological abnormalities are mainly seen in anencephaly, spina bifida and other neural tube defects, and structural abnormalities of the digestive tract are mainly esophageal as well as duodenal atresia, which prevents the fetus from swallowing amniotic fluid, resulting in amniotic fluid accumulation and excessive amniotic fluid; 2. Multiple pregnancies: the incidence of excessive amniotic fluid in twin pregnancies is 10 times higher than that in singleton pregnancies, and monochorionic twin pregnancies with huge amniotic fluid may also be complicated by twin fetal transfusion syndrome, where the recipient of this blood increased circulating blood volume and urine volume, resulting in excessive amniotic fluid; 3. Placental cord lesions: If the diameter of placental chorionic villous hemangioma is greater than 1.01 cm, 15%-30% of patients will be combined with excessive amniotic fluid. In addition, giant children and umbilical cord sail attachment can also lead to excessive amniotic fluid; 4. Pregnancy complications: such as gestational diabetes, maternal and child blood type incompatibility, fetal immune edema, etc. can affect fluid exchange and lead to excessive amniotic fluid.