Whether amniotic fluid of 3.9 in 24 weeks of pregnancy is normal or not depends on whether it is the depth of amniotic fluid or the amniotic fluid index, if it is the depth of amniotic fluid of 3.9cm is normal, if it is the amniotic fluid index of 3.9cm then it is the amniotic fluid that is too low. Amniotic fluid is an important indicator to assess the health of the fetus. Under normal circumstances the maximum amniotic fluid dark zone vertical depth >8cm is too much amniotic fluid, ≤2cm is too little amniotic fluid. If the depth of amniotic fluid measured at 24 weeks of pregnancy is 3.9cm it is normal. Other indicators for assessing the amount of amniotic fluid include the amniotic fluid index, which refers to the division of the abdomen into four quadrants, the maximum vertical depth of the dark zone of amniotic fluid in each quadrant is added up, >20cm for too much amniotic fluid, ≤5cm for too little amniotic fluid. If the index of amniotic fluid measured at 24 weeks of pregnancy is 3.9cm, it is considered that the amniotic fluid is too small, this situation is not normal, and it is recommended to go to the hospital in time. If the amount of amniotic fluid is abnormal during pregnancy, it is recommended to visit the obstetrics department of the hospital in a timely manner to find out the cause of the abnormal amniotic fluid and to assess the growth and development of the fetus at the same time. If necessary, further tests should be performed for evaluation.