According to the teratogenic situation of drugs to embryo and fetus, FDA classifies the level of harmfulness of drugs to embryo and fetus into 5 levels: A, B, C, D and X. 1.Grade A After clinical control study, it cannot be confirmed that the drug has harmful effects on fetus in early and middle and late pregnancy, and has the least possibility of harming embryo and fetus, and is a non-teratogenic drug. Such as moderate amount of vitamins. 2.B Grade No harmful effects on embryo and fetus can be seen after animal experimental research. No clinical control experiment, no harmful evidence was obtained. Can be used under the observation of physicians. Such as penicillin, erythromycin, digoxin, insulin, etc. 3.Class C Animal experiments show adverse effects on embryo and fetus. Since there is no clinical control evidence medical education. The drug can only be used with caution when the benefits to the pregnant woman, the potential benefits to the embryo and fetus, and the harm to the embryo and fetus are fully weighed. For example, gentamicin, promethazine, isoniazid, etc. 4.Grade D There is sufficient evidence of harm to the embryo and fetus. Consider using only if the pregnant woman has a life-threatening or serious disease and other drugs are ineffective. Such as streptomycin sulfate, tetracycline hydrochloride, etc. 5. X-rated Various experiments have confirmed that it will cause embryonic and fetal abnormalities. Use is prohibited during pregnancy. Such as methotrexate, hexenestrol, etc. In the first 12 weeks of pregnancy, it is better not to use Class C, D or X drugs.