The reasons for the decrease in amniotic fluid mainly include the decrease in production and the increase in outflow. 1. Decrease in production: In early pregnancy, amniotic fluid is mainly the dialysate of maternal serum that enters the amniotic cavity through the placenta, so the production of amniotic fluid decreases when there are problems with the placenta. After the middle of pregnancy, the source of amniotic fluid is mainly fetal urine. If the amount of urine decreases due to fetal kidney disease and other aspects, amniotic fluid will decrease. 2. Increased outflow: Amniotic fluid is generally not outflow during pregnancy, but if there is premature rupture of membranes and other circumstances, it will lead to outflow of amniotic fluid, and amniotic fluid naturally decreases after outflow. Clinical amniotic fluid is a bad thing for the pregnant woman and the fetus, so you need to take regular checkups to understand the situation of amniotic fluid, if there is a decrease in amniotic fluid, you must consult a doctor in a timely manner, to clarify the specific causes of amniotic fluid, and under the guidance of the doctor to give targeted treatment.