Pregnant women can lie flat, there is no effect of lying flat at the beginning of pregnancy, you can lie flat at the middle and late stages of pregnancy, but the time of lying flat should not be too long. Early pregnancy, the development of the gestational sac is relatively small, the uterus has not protruded from the pelvis, at this time there is no high demand for sleeping posture, you can lie down to sleep, there is no restriction on the time of lying down to sleep, try to feel comfortable as appropriate. In the middle and late stages of pregnancy, with the increase of pregnancy weeks, the uterus will gradually increase in size, you can lie flat to sleep, but the time of lying flat should not be too long, lying flat for too long will increase the pressure of the abdomen, is not conducive to blood circulation, and is not good for the growth and development of the fetus. Compression of the inferior vena cava causes low blood pressure, manifesting symptoms such as nausea, dizziness, and difficulty in breathing. Try to choose the left lateral position to sleep in the middle and late stages of pregnancy, and when you are tired of the left lateral position, you can change to the right lateral position or supine position, but the time should not be too long, and you should turn over appropriately. After pregnancy to ensure adequate sleep, try to avoid staying up late at night.