Early pregnancy pregnant women lying flat will not lead to fetal hypoxia, late pregnancy pregnant women lying flat may lead to fetal hypoxia, clinical reports say lying flat for 2 hours can lead to fetal hypoxia, but the specific time has individual differences. In late pregnancy, with the gradual increase of fetal size, the long time lying flat will cause the fetus to compress the inferior vena cava of the pregnant woman, resulting in poor blood circulation of the pregnant woman and rapid decrease in the amount of cardiovascular blood, which will cause fetal hypoxia. Therefore, pregnant women in the late stage is not recommended to lie flat, but if the plain habit of sleeping in a flat position, and the flat position during pregnancy is not any discomfort, it is not necessary to overly entangled and lead to affect sleep. Specific lead to fetal hypoxia lying flat time varies from person to person. Pregnant women should avoid keeping the same action for a long time during pregnancy, and try to keep the left side lying position in the middle and late stages to avoid the right-rotated uterus compressing the inferior vena cava. In addition, pregnant women should avoid being sedentary to prevent obstruction of inferior vena cava reflux. Although pregnant women often change positions for their own comfort during pregnancy, they should pay attention to gentle movements and try to stay in the left lateral position in the middle and late stages.