The amniotic fluid index is the maximum vertical depth of the four quadrants of the uterus, and then the amniotic fluid index is added up. Amniotic fluid index between 8-25 cm is normal, <8 cm is low amniotic fluid, <5 cm is too little amniotic fluid, >25 cm is too much amniotic fluid. The general incidence of excessive amniotic fluid monitored by ultrasound is about 0.5%-1%. Amniotic fluid index between 25-35cm is mild excess, between 35-45cm is moderate excess, and over 45cm is severe excess. Excessive amniotic fluid is caused by fetal malformations of the digestive tract and nervous system, as well as maternal causes, including gestational diabetes, multiple pregnancies and umbilical cord placenta. Low amniotic fluid is also monitored by ultrasound, between 5-8cm is low amniotic fluid, below 5cm is low amniotic fluid, usually low amniotic fluid is more dangerous. If it is severe amniotic fluid, such as below 5cm or even 2cm, the mortality rate for having a perinatal baby will be greatly increased and can even reach more than 80% mortality.