The maximum depth of the dark zone of amniotic fluid is generally 3-7 cm. in recent years, the measurement of amniotic fluid is more accurate due to the clear diagnosis of ultrasound. the diameter of the maximum amniotic pool measured by B-mode ultrasound during 28-40 weeks under ultrasound is generally between 3 and 7 cm. Therefore the measurement of the maximum amniotic pool with the uterine contour perpendicular to the depth, that is, the maximum depth of the dark area of amniotic fluid ≦ 2cm is too little amniotic fluid; the depth ≦ 1cm is severe amniotic fluid; the depth ≥ 7cm is too much amniotic fluid. So the measurement of amniotic fluid under ultrasound is a good guide for our clinicians to observe the health of the baby. If the amniotic fluid is too much or too little, the doctor will usually give some suggestions, and the pregnant mother must pay attention to the good fetal movement, listen to the doctor’s arrangement, and conduct the ultrasound examination.