Some pregnant women like to sleep flat on their backs. In early pregnancy, the uterus is small, and sleeping flat on the back generally has no effect on the pregnant woman and the fetus, but in the middle and late stages of pregnancy, sleeping flat on the back will not only cause discomfort to the pregnant woman, but also affect the development of the fetus, and it is not recommended to sleep flat on the back. In the early stages of pregnancy, the fetus is small, lying flat to sleep will not bring adverse reactions. However, in the middle and late stages of pregnancy, as the uterus grows, it presses on the inferior vena cava, which leads to a decrease in cardiac output, and pregnant women may experience dizziness and discomfort. In addition, due to the decrease in blood supply to the placenta, it is not conducive to the supply of nutrients to the fetus, which will affect the growth and development of the fetus in the long run. No matter what kind of sleeping position a pregnant woman adopts, she needs to ensure that she gets enough sleep first, and on the basis of sufficient sleep, adopting a suitable sleeping position is more conducive to the development of the fetus. Pregnant women should also go to the hospital for regular checkups to ensure that the fetus is in a normal state of growth and development.