The amniotic fluid depth of 40mm is a normal value. After pregnancy, pregnant women need to undergo maternity checkups, and ultrasound is often done, so ultrasound observation of the baby’s health has many indicators, and amniotic fluid is one of them. In the ultrasound observation, there are two indicators of amniotic fluid, the first is the maximum depth of amniotic fluid, and the other is the index of amniotic fluid. The maximum depth of amniotic fluid is generally 30mm-70mm, so 40mm is the normal amniotic fluid depth. The amniotic fluid index is a vertical line drawn through the belly button of the pregnant woman and divided into 4 quadrants, each quadrant, the value of the maximum depth of amniotic fluid and that is the amniotic fluid index. The normal amniotic fluid index is 8cm-10cm, or 80mm-180mm, so if a pregnant woman’s amniotic fluid depth is 40mm, this value is normal.