The difference between the amniotic fluid units cm and mm is that one represents centimeters and the other millimeters. The amniotic fluid index is the sum of amniotic fluid measurements in the four quadrants of the uterus. Its cm stands for centimeters and mm stands for millimeters. Using the umbilical level and the white line of the abdomen as markers, the uterus is divided right-angled into four quadrants: upper left, upper right, lower left and lower right. Measurements can be made in centimeters or calculated in millimeters. The normal range of amniotic fluid index is 8-22cm, or 80mm-220mm. amniotic fluid index during pregnancy can be in the normal range, the two indexes are calculated in different units, the value is normal means that the fetus’s amniotic fluid index is normal. You should pay attention to rest during pregnancy and do your labor checkups on time.