Sleeping flat on your back is not recommended in late pregnancy. In the early and middle stages of pregnancy, you can lie flat on your back and it usually does not cause too much effect. In late pregnancy, the uterus enlarges and rotates to the right, and if you lie down for too long, the uterus may compress the inferior vena cava, reducing blood flow to the uterus, which may lead to fetal ischemia and hypoxia. In late pregnancy, should reduce the time of lying down to sleep, in late pregnancy, should take more side lying position rest, preferably left side lying position, but do not keep a position too long, should be left side lying position and right side lying position alternately, to avoid the left side or right side of the muscle to cause excessive compression. In the late stages of pregnancy, pregnant women should also take reasonable rest, avoid strenuous exercise, regular medical checkups to prevent abnormalities.