When medication is used during pregnancy, most of the drugs can pass through the placenta. Since the fetus is in the process of growth and development, its physiological condition is different from that of adults, and if pregnant women use drugs improperly, it may cause adverse effects on the fetus and the newborn, including death, teratogenicity, or damage to fetal organs and abnormal functions. However, if no medication is administered to a pregnant woman who is ill without analysis, it may also affect the fetus directly or indirectly as a result. The use of drugs during pregnancy is described below. The principles of drug use during pregnancy: 1. Avoid unnecessary use of drugs, including health care drugs, during pregnancy. 2. Consider the use of drugs according to the size of the gestational week, i.e., the period of fetal development required, such as within the third month of pregnancy is an important period of fetal organ development, the use of drugs should be particularly careful, and treatment can be postponed until after this period as far as possible. For example, for hyperthyroidism combined with pregnancy, the following procedures can be used: sedative (Valium), beta-blocker (Cotilobert), and antithyroid metabolizer (propylthiouracil). When new drugs and old drugs are effective at the same time, avoid using new drugs that have not yet been determined to have adverse effects on the fetus, and avoid using large doses of drugs when small doses can be used. 5.When pregnant women have to use drugs in emergencies, they should try to use Class A and B drugs that are clinically proven not to have teratogenic effects for many years. The U.S. Food and Drug Administration classifies the drug completeness during pregnancy into 5 classes. class A drugs are completely safe for pregnant women and are harmless to embryo and fetus, such as moderate amount of vitamin A, B1, B2, C, D, E, etc.; class B drugs are safe for pregnant women and are basically harmless to fetus, such as penicillin, erythromycin, digoxin, insulin, etc.; class C drugs are only proved to be teratogenic to fetus or can kill fetus in animal experimental research. Class C drugs are only proven to be teratogenic to the fetus or can kill the embryo in human studies, so pregnant women need to weigh the pros and cons and confirm that the pros outweigh the cons before applying them; Class D drugs have definite evidence of harm to the fetus, so unless pregnant women have absolute effect after using them, they should not be considered for application; Class X drugs can make the fetus abnormal and are prohibited during pregnancy. 6.To prevent drug-induced fetal abnormalities, Class C and D drugs should not be used in the first three months of pregnancy (evidence of harm in animal C and human D). 7, pregnant women in rescue and other special circumstances when using C, D drugs, should be given a true and exact description. For example, if anaphylaxis caused by serum products, when calcium gluconate (class A) and paracetamol (class B) are given to be ineffective, flupromazine (class C) and dexamethasone (class D) have to be used so as to effectively control the condition.