Pregnant women can sleep in any position during early and mid-pregnancy. In late pregnancy, due to the gradual increase in the size of the fetus, you can use the left side of the sleeping position. Pregnant women in early and mid-pregnancy, the size of the fetus has not increased significantly, at this time, even if the use of supine sleeping position, will not produce pressure on the pregnant woman. However, in late pregnancy, due to the gradual increase in fetal size, supine position, the enlarged uterus may compress the inferior vena cava, resulting in pregnant women to reduce the amount of cardiac blood, affecting the blood supply of the placenta, so it is best to use the side of the sleeping position. Although the left side and right side of the sleeping position can be used, but the pregnant woman is best to use the left side of the lying position, because the uterus is often disturbed by the sigmoid colon and right rotation, the left side of the lying position can be partially corrected uterine right rotation.