Allylestrenol tablets belong to the estrogen class of drugs, the principle of fetal preservation is to enhance the chorionic villous membrane activity, promote the secretion of endogenous progesterone and HCG, to promote the normalization of placental function, elevate the concentration and activity of the enzyme oxytocin, lower oxytocin levels; increase the uterine excitation threshold, antagonize the stimulating effect of prostaglandins on the uterus, the drug does not have an adverse effect on the embryo and the fetus, and therefore is suitable for full-term fetal preservation. Allyl estradiol can mainly treat preeclampsia, habitual abortion, preterm labor and other diseases, with certain effect of birth preservation. Adverse effects such as fluid retention, nausea and headache are occasionally seen. The drug is contraindicated in patients with severe liver disease and Rotor syndrome. The drug is used with caution in patients with heart disease and kidney disease to avoid sodium retention. In addition, pregnant women with diabetes should pay attention to regular blood sugar testing because the drug can reduce glucose tolerance. Note that the drug should be used under the guidance of a doctor, avoid unauthorized use of the drug to avoid adverse effects. If the above symptoms occur after the use of the drug in pregnant women, it is recommended to seek medical attention in time, under the guidance of the doctor, improve the relevant examination, clarify the cause of the disease and symptomatic treatment.