The normal value of amniotic fluid in the third trimester is 300-2000 ml. However, the specific amount of amniotic fluid before delivery cannot be measured, and only ultrasound can be used to measure the depth of amniotic fluid. There are two indicators for ultrasonic measurement of amniotic fluid volume, one is the maximum amniotic fluid pool depth, and the other is the amniotic fluid index. The amniotic fluid index is to measure the maximum amniotic fluid pool depth in four quadrants of the uterus respectively, and then the sum of the four values is called the amniotic fluid index. The normal value of amniotic fluid index in the third trimester is 8-25 cm. Less than 8 cm is oligohydramnios, less than 5 cm is oligohydramnios; More than 25 cm, it is amniotic fluid; Among them, 25-35cm is mild polyhydramnios, 36-45cm is moderate polyhydramnios, and more than 45cm is severe polyhydramnios. Therefore, the normal value of amniotic fluid index at 37 weeks is 8-25 cm.
