Flat sleep is also known as lying down, late pregnancy can lie down for a short period of time, should not be too long lying down. After 28 weeks of pregnancy belongs to the late stage of pregnancy, at this time the fetus in the uterus grows and develops faster, the uterus is also more obvious, occasionally lying down to sleep does not have much effect, long time lying down to sleep the uterus may compress the inferior vena cava of the blood return, the blood can not return to the heart in time, the whole body does not have enough blood supply, causing postural hypotension, dizziness, fatigue, nausea, vomiting and other discomforts. Symptoms. After 28 weeks of pregnancy, try to sleep on the left side of the bed, the uterus will be in a right-handed position after the uterus enlarges in late pregnancy. Lying on the left side may improve the right rotation of the uterus and provide the placenta with more adequate blood oxygen, which is more conducive to the growth and development of the fetus in the uterus. Late pregnancy should be based on individual circumstances, try to choose a comfortable position, so as not to affect the quality of sleep.