Pregnant women can sleep flat on their backs, but it is best not to sleep flat for long periods of time. There are no clear rules for pregnant women to sleep in a comfortable position, and they can change their positions. However, in late pregnancy, when lying on the back, the increasing uterus compresses the inferior vena cava, resulting in obstruction of venous return, reducing the volume of return blood, reducing the volume of cardiac output and leading to a drop in blood pressure, resulting in the formation of supine hypotension syndrome, pregnant women will have dizziness, chest tightness and other uncomfortable feelings. Side-lying position can lift the uterine compression and improve blood flow. Therefore, it is better to sleep in the side-lying position in the middle and late stages of pregnancy. Since the uterus is more right-rotated in pregnancy, the left side lying position is better. If the long time left side lying pregnant women uncomfortable can also be changed to the right side lying. After pregnancy, women must do regular checkups, and listen to the obstetrician’s guidance in life and diet.