An amniotic fluid index of 5.1cm is dangerous. The value of amniotic fluid usually ranges from 5 to 18cm, and less than 5cm indicates that the pregnant woman has insufficient amniotic fluid. If the amniotic fluid index is 5.1 and does not rise within a short period of time, it is important to go to the hospital in time for relevant testing and monitoring to avoid certain risks to the fetus. Amniotic fluid plays a protective and cushioning role, which can reduce the impact of the fetus and the abdominal wall. Insufficient amniotic fluid will cause the fetus to have difficulty in breathing and will also affect the development of the fetus’s lungs. After the buffering effect of amniotic fluid disappears, it will be subjected to the pressure of the uterus, which will cause the adhesion of the limbs and the body in serious cases. If you have low amniotic fluid during pregnancy, you can drink more water, which can promote blood circulation, increase the blood supply to the placental area and increase the amount of amniotic fluid.