In the 3rd month of pregnancy, a pregnant woman can sleep flat on her back and remain in the flat position if she is not uncomfortable. However, the uterus after the third month of pregnancy will be slightly rotated to the right, the right rotation of the uterus on the inferior vena cava and abdominal aorta to form compression. As the month of pregnancy increases, the pregnant woman’s abdomen gradually bulges, and sleeping flat on the back will cause abdominal compression, which will easily cause insufficient blood supply and is not conducive to the healthy development of the fetus. In order to alleviate the impact of sleeping position on the fetus, pregnant women try to choose the left side lying position when sleeping. The left side position can avoid the pressure of the enlarged uterus on the blood vessels in the abdominal cavity, and at the same time improve the blood supply to the uterus. However, it also depends on the condition of each pregnant woman, some pregnant women feel uncomfortable to sleep on the left side, occasionally the right side of the bed can also be.