Amniotic fluid of 40mm is normal. In late pregnancy, the normal depth of amniotic fluid is 3-8cm, if it is below 3cm it is too little amniotic fluid, and if it is more than 8cm it is too much amniotic fluid. If you use the amniotic fluid index to calculate, that is, take the umbilicus as the center, draw a cross, and add up the maximum depth of amniotic fluid in each quadrant, if it is more than 25cm, it is too much amniotic fluid, if it is less than 8cm, it is less amniotic fluid, and if it is less than 5cm, it is too little amniotic fluid. If you have too much or too little amniotic fluid, you should find out the cause as soon as possible. If you have too little amniotic fluid in the late stages of pregnancy, you should end the labor as soon as possible, otherwise it will have an effect on the baby.