The painful uterine contractions make the maternal sympathetic nerves excited and increase the secretion of catecholamines in the body, thus increasing the blood pressure. In addition, uterine contractions can significantly reduce the blood flow and blood volume of the uterus, which relatively increases the blood volume of the circulation, which may also increase blood pressure. For pregnant women it is easy to be affected by the change of position, which 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.