The sudden high and low blood pressure of pregnant women may be caused by changes in sympathetic excitability. In late pregnancy, pregnant women may experience regular or irregular contractions, and painful uterine contractions cause maternal sympathetic excitation and increased secretion of catecholamines in the body, thus increasing blood pressure. In addition, uterine contractions can cause a significant reduction in blood flow and blood volume in the uterus and a relative increase in circulating blood volume, which may also increase blood pressure accordingly. For pregnant women it is easy to suffer from postural changes that can cause postural hypotension. Therefore, changes in sympathetic excitability and changes in the position of the pregnant woman causing hypotension are factors associated with greater fluctuations in the patient’s blood pressure.