After a woman is pregnant, the fetus grows gradually in the uterus, the original uterus like an inverted pear-shaped size becomes the size of a watermelon at full-term pregnancy, the volume of the uterus increases from 5 ml when not pregnant to 5000 ml at full-term, and the weight of the uterus increases from 50 g when not pregnant to 1000 g at full-term pregnancy. As the uterus and the fetus grow, the sleeping position of the pregnant woman becomes more and more important, especially in the late stage of pregnancy, i.e. 7-9 months of pregnancy, the poor sleeping position of the pregnant woman will not only affect the position of the uterus, but also increase the pressure of the pregnant uterus on the surrounding tissues and organs and affect the blood flow to the uterus and the placenta. The fetus is exchanging gases and substances with the mother through the placenta to obtain oxygen, nutrients, and expel carbon dioxide and waste. The adequacy of placental blood flow is crucial to the growth and development of the fetus. Therefore, the sleeping posture of pregnant women has been confirmed after long-term clinical research and practice: pregnant women in pregnancy, especially in late pregnancy, take the left side lying position is the best sleeping position for pregnant women. 1, the left lateral position can reduce the pressure of the enlarged pregnant uterus on the aorta and skeletal artery of pregnant women, which can maintain the normal blood flow of the uterine artery, ensure the blood supply of the placenta, and provide the fetus with the nutrients required for growth and development. 2.Left side lying can reduce the compression of the pregnant uterus on the inferior vena cava and increase the blood flow back to the heart. The increase in the amount of blood returning to the heart can increase the blood flow to the kidneys and improve the blood supply to the brain tissue, which is conducive to avoiding and reducing the occurrence of gestational hypertension syndrome. The supine position of the sleeping position of pregnant women: the greatest impact on pregnant women and fetuses, a long time will compress the abdominal aorta behind the uterus, affecting the blood supply of the uterus, resulting in a lack of nutrition for the fetus, may also affect the blood supply of the kidneys, resulting in a reduction in urine, toxic substances can not be excreted in a timely manner, causing pregnancy poisoning, increased blood pressure, swelling of the lower limbs and vulva, serious convulsions, coma, and even May be life-threatening, pregnant women sleeping on their backs, may also compress the inferior vena cava behind the uterus, so that the return flow of blood to the heart is reduced, affecting the lack of blood and oxygen supply to the brain, pregnant women will appear dizzy, chest tightness, pale, nausea and vomiting and other situations. Pregnant women sleeping position of the right side: will make the uterus is different degrees of rotation to the right. In this way, the ligaments and ties that maintain the normal position of the uterus will be under tension. The blood vessels in the ligament are strained, affecting the blood supply to the fetus, causing chronic fetal hypoxia and, in severe cases, fetal asphyxia and death. The best sleeping position for pregnant women is the left lateral position, which allows the right-sided uterus to shift to a straight position, thus reducing the resulting abnormal fetal position and delivery. It can also avoid the compression of the uterus on the inferior vena cava, increase the cardiac blood expulsion of pregnant women, reduce swelling, improve the blood perfusion of the uterus and placenta, which is conducive to reducing preterm labor and avoiding the compression of the uterus on the kidneys, thus contributing to the growth and development of the fetus and eugenics.