Pregnant women generally lie on their left side during pregnancy because the uterus has a mild rightward rotation during pregnancy, and lying on the left side improves this rightward rotation and improves compression of the inferior vena cava by the uterus in late pregnancy. As the weeks of pregnancy increase, the size and weight of the uterus will gradually increase; the uterus in late pregnancy will have a mild rightward rotation, increase in blood volume, endocrine changes and other factors lead to the enlarged uterus compression of the inferior vena cava, preventing venous blood flow back to the heart, resulting in increased venous pressure. This will lead to varicose veins and lower extremity edema in the long run. Sleeping on the left side can improve blood flow to the lower extremities and maintain stable blood pressure. Therefore, pregnant women in late pregnancy can properly choose the left lateral position to improve the lower limb edema, but also to ensure the normal blood supply of the placenta.