Lying flat at the beginning of pregnancy will not lead to fetal hypoxia, and occasionally lying flat in the middle and late stages of pregnancy will not lead to fetal hypoxia, while lying flat for a long time in the late stages of pregnancy may lead to fetal hypoxia. In early pregnancy, the uterus does not enlarge significantly, and the fetus is also relatively small, lying down will not lead to a decrease in aortic blood flow, and will not cause intrauterine oxygen deprivation of the fetus. The uterus in the middle and late stages of pregnancy is in a right-handed state, and occasional lying down will not lead to fetal hypoxia, but prolonged lying down in the late stages of pregnancy may lead to fetal hypoxia. The oxygen supply to the fetus comes from the uterine artery, a branch of the aorta of the pregnant woman. When the blood flow to the aorta decreases, the blood flow to the uterus and placenta decreases accordingly, and the fetus may become hypoxic. In late pregnancy, as the uterus enlarges, the weight and size of the uterus compresses the aorta, and when the pregnant woman lies down for a long time, the uterus compresses the inferior vena cava for a longer period of time, which causes a decrease in return flow, and in turn causes fetal hypoxia. Fetal hypoxia may be manifested by abnormal fetal movements, pregnant women should keep track of fetal movements, abnormalities require hospital ultrasound and fetal heart monitoring to find out whether fetal hypoxia in the womb.