If you sleep flat on your back in late pregnancy, it may have an effect on the fetus, such as obstruction of placental blood supply, fetal hypoxia, and fetal intrauterine distress. 1. Obstructed blood supply to the placenta: when lying flat, the enlarged uterus compresses the inferior vena cava, affecting the return of blood flow, resulting in postural hypotension, which affects the supply of oxygen to the brain, and is prone to panic attacks, chest tightness, dizziness and other discomforts that can also affect the blood supply to the uterus and the placenta and the supply of oxygen. 2. Fetal hypoxia: If you sleep flat on your back in late pregnancy, it may cause fetal hypoxia, fetal hypoxia is a very dangerous situation, so in late pregnancy, mothers-to-be should insist on counting the fetal movements, such as the discovery of fetal movement irregularity, we must go to the hospital in a timely manner. 3. Fetal intrauterine distress: If you sleep flat on your back in late pregnancy, it may cause fetal intrauterine distress. Pay attention to fetal movement, do fetal heartbeat monitoring, and regular obstetric examination in late pregnancy to observe the baby’s health in time. Try not to sleep flat on your back in late pregnancy, lie on your left side, and if you are uncomfortable for a long time, you can adopt the position of lying on your right side. Pregnancy is a very hard process. Expectant mothers also to the late pregnancy not only to pay attention to the sleeping position, but also adhere to the counting of fetal movement, regular obstetric examination. If necessary, timely medical treatment.