Sleeping on the left side of the pregnancy can maintain uterine artery blood flow, improve uterine rotation, and increase the amount of return blood. 1. Maintain uterine artery blood flow: the uterus gradually increases in the middle and late stages of pregnancy, sleeping on the left side can reduce the pressure of the growing pregnant uterus on the pregnant woman’s aorta, and can maintain the normal uterine artery blood flow to provide the placenta with sufficient blood oxygen, which is conducive to the growth and development of the fetus. 2. Improve the uterus right: after pregnancy with the development of the fetus, the pregnant woman’s uterus gradually increase or shift to the right side of the rotation, will produce a certain amount of pressure on the surrounding organs and tissues, such as compression of blood vessels affecting the fetus oxygen, nutrients delivery. Choosing to sleep on the left side can improve the state of the uterus rotating to the right, so that the uterus and the surrounding organs and tissues to maintain a balanced state, reduce the uterine vascular tension, increase placental blood flow, which is conducive to the growth and development of the fetus. 3. Increase the amount of return blood: you can’t sleep on your back for a long time after the middle and late stages of pregnancy, which will directly compress the inferior vena cava and the abdominal aorta, making the amount of return blood and the amount of cardiac output insufficient, resulting in insufficient blood supply and nutrients to the mother and fetus, and manifesting symptoms such as dizziness, palpitations, nausea, vomiting and other discomforts. Choosing to sleep on the left side can reduce the pressure on blood vessels, increase the amount of blood returning to the heart, and supply oxygen and nutrients to the fetus. After late pregnancy, try to choose the left side to sleep, but the sleeping position should still try to make the pregnant woman feel comfortable as appropriate.