Pregnant women do not stipulate how many months can not lie flat, a whole pregnancy can lie flat to sleep, only the middle and late stages of pregnancy is best not to lie flat for a long time to sleep. The early trimester of pregnancy does not have very high requirements for sleeping posture, at this time the development of the fetus is relatively small, the uterus is not obvious, has not yet protruded from the pelvis, lying down to sleep on the fetus and the pregnant woman will not cause a major impact. Late in pregnancy with the increase in pregnancy weeks and fetal development, the uterus will gradually increase, you can sleep flat for a short period of time, try not to lie down for a long time, late for a long period of time, lying down when the pregnant woman’s uterus will be compressed to the large blood vessels, affecting the venous return of the lower limbs, may be low blood pressure, dizziness and other uncomfortable symptoms. Sleeping posture after pregnancy should also try to feel comfortable as appropriate, sleeping posture is not good may affect the quality of sleep.