Amniotic fluid is the fluid in the amniotic cavity of the uterus. Too much amniotic fluid is not good for the growth of the fetus. What are the causes of excessive amniotic fluid? What are the risks to the mother and child? What should be done? Amniotic fluid is the fluid in the amniotic cavity of the uterus, which is an essential component to maintain the life of the fetus during pregnancy. Amniotic fluid comes mainly from the mother’s serum, the fetus’ urine, respiratory system, and gastrointestinal secretions. The amount of amniotic fluid generally varies from 300-2000 ml as the weeks of gestation change. Too much or too little amniotic fluid is detrimental to the growth of the fetus. Amniotic fluid in excess of 2000 ml is called hyperhydramnios, with an incidence of 0.5%-2%. The diagnosis is usually determined using ultrasound measurement of the amniotic fluid index and amniotic fluid volume, and the prognosis depends on its etiology and the severity of the disease. The role of amniotic fluid during pregnancy is that the fetus grows in the amniotic fluid, which cushions external pressure and of course reduces the discomfort caused to the mother when the fetus moves around in the uterus. The amniotic fluid creates an airtight greenhouse that maintains a relatively constant temperature for the growing fetus. The amniotic fluid expands the space for the fetus to move around in the uterus, which helps the fetus to grow and develop normally. In addition, amniotic fluid also contains antibacterial substances, which have a certain anti-infective effect. After labor, the amniotic fluid forms water sacs, which can promote the dilation of the cervix. During uterine contractions, amniotic fluid can cushion the pressure of the uterus on the fetus, especially on the fetal head. After rupture of membranes, amniotic fluid can lubricate the birth canal and facilitate the delivery of the fetus. The causes of excess amniotic fluid are only present in 17% of mild cases of excess amniotic fluid, while in 91% of moderate and severe amniotic fluid pregnancies, there is an underlying condition. Fetal anomalies and genetic disorders account for 8-45% of cases, with central nervous system and digestive tract anomalies being the most common, especially digestive atresia and myotonic dystrophy leading to fetal swallowing abnormalities; gestational diabetes mellitus accounts for about 5-26% of cases, with poor glycemic control often leading to giant babies and excessive amniotic fluid, probably due to osmotic diuresis caused by hyperglycemia, resulting in increased amniotic fluid; multiple pregnancies account for 8-10 The incidence of hyperhydramnios in twin pregnancies is about 10 times higher than in singleton pregnancies; fetal anemia due to maternal-fetal blood group incompatibility may also affect fluid exchange; other causes include viral infections, maternal hypercalcemia, and placental abnormalities. Other causes include viral infections, maternal hypercalcemia, and placental abnormalities. The risk to the mother and fetus is often accompanied by the presence of underlying disease in the mother or fetus, and therefore can have a detrimental effect on both mother and fetus. Excessive amniotic fluid can cause placental overdistension and increase obstetric complications such as maternal respiratory distress, preterm labor, premature rupture of membranes, abnormal fetal previa, umbilical cord prolapse, postpartum hemorrhage, placental abruption, hypertension during pregnancy and urinary tract infection. The risk of these complications varies depending on the etiology of the excess amniotic fluid. In addition to the possible impact on maternal and fetal health in the perinatal period, excessive amniotic fluid can also have long-term effects on child growth and development. A retrospective cohort study published in the Journal of Pediatrics showed that excess amniotic fluid during pregnancy, confirmed by ultrasound, not only increased the risk of cesarean delivery and macrosomia, but also significantly increased the risk of postnatal fetal malformations, genetic disorders, neurological abnormalities, and developmental delays. The management of excessive amniotic fluid is usually diagnosed by ultrasound. The management requires consideration of the gestational week, the presence of fetal malformations and the severity of the disease. The first step is to actively treat the cause, such as gestational diabetes mellitus, gestational hypertension and maternal-fetal blood group incompatibility; for severe symptoms, an appropriate amount of amniotic fluid can be released by ultrasound-guided transabdominal amniocentesis to relieve symptoms; prostaglandin synthase inhibitors (such as indomethacin) have anti-diuretic effects and can reduce the amount of amniotic fluid by inhibiting fetal urination, but they should not be used for a long time.