Magnesium sulfate has an antispasmodic effect and is used for birth control usually for no more than five days. Magnesium sulfate can relieve smooth muscle spasm, the uterine muscle is composed of smooth muscle, the uterus is contracted before the delivery period, that is, the uterine smooth muscle spasm. Pregnant women may experience abdominal pain, vaginal redness and other symptoms, which may lead to the risk of fetal hypoxia, preterm labor or even preterm delivery. At this time, the patient can be given magnesium sulfate static drip to release the smooth muscle spasm, so as to achieve the effect of fetal preservation. But magnesium sulfate overdose will have certain side effects, such as flushing, sweating, dry mouth and other symptoms, if the infusion rate is relatively fast, it will also lead to nausea, vomiting; serious cases will also lead to respiratory failure, cardiac arrhythmia; prolonged use of magnesium sulfate may also cause constipation, and even paralytic intestinal obstruction. Therefore, it is recommended that pregnant women use magnesium sulfate slowly IV, and not for a long time, the specific should follow the doctor’s instructions.