The causes of low blood pressure during pregnancy are considered as follows: First, hypotension caused by nausea, vomiting and loss of appetite in early pregnancy. Second, recumbent hypotension, because the gradually expanding uterus compresses the inferior vena cava when the pregnant woman is in the recumbent position, resulting in the obstruction of blood return causing hypotension. Third, postural hypotension, because pregnant women stand up quickly from a sitting or squatting position, the blood supply to the brain is insufficient, causing a drop in blood pressure. Fourth, combined with other organ system lesions. In addition, as the gestational week increases, the diaphragm is compressed by the enlarged uterus, resulting in nerve excitation, which slows the heart rate and lowers blood pressure. Blood pressure levels are related to many factors, including its central output, circulating blood volume, peripheral vascular resistance, blood viscosity, and vascular elasticity, all of which can cause a decrease in blood pressure.