Improper use of medication during pregnancy may have an impact on the fetus, and the World Health Organization estimates that more than 90 per cent of pregnant women have taken a variety of prescription drugs, over-the-counter medications or banned drugs during pregnancy. Among children with birth defects, 2% to 3% are caused by drugs, while most of the rest are caused by genetic and environmental factors. Drugs should be used with caution during pregnancy. Pregnant women and fetus through the placenta to achieve the exchange of substances, most drugs can enter the body of the fetus through the placenta, especially some fat-soluble large and small molecules of the drug is more likely to be transferred into the body of the fetus through the placenta, the drug can also be swallowed by the fetus amniotic fluid from the gastrointestinal absorption of a small amount. In addition, due to the imperfect development of fetal liver, drug metabolism enzyme deficiency, the detoxification ability of the drug is low, fetal glomerular filtration rate is low, drug and degradation product excretion is delayed, so the drug is easy to accumulate in the fetal body. Therefore, drugs are prone to affect the fetus. The effect of drugs on the fetus depends on the developmental stage of the fetus at the time of drug administration, and the consequences of drug administration at different times are different: 1) Pre-fertilization to the end of the 4th week of gestation: the effect of drugs on the embryo during this period is “all” or “none”. “All” that is, harmful drugs can destroy all or part of the embryonic cells, resulting in early death of the embryo, leading to miscarriage; “no” that is, harmful drugs did not damage the embryo or only damage a small number of cells, but the cells in this period of time have the ability of multi-directional differentiation, which can compensate for, and repair the damaged cells, and the embryo can still continue to live. However, the cells in this period have the ability of multi-directional differentiation, which can compensate and repair the damaged cells, and the embryo can still continue to develop without any abnormality. Therefore, this period belongs to the safe period of using drugs, if the drugs do affect the fertilization rate, it will be eliminated naturally before the implantation. 2) 4th to 9th week of pregnancy: This is the period when the important organs of the fetus, such as the central nervous system, heart, eyes, limbs, etc., begin to form, and it is also the period that is most sensitive to medication, and the fetus is very susceptible to the influence of medication and other external factors that may lead to malformations. 3) 10th week of pregnancy to delivery: this period is the stage of fetal growth and functional perfection, but the nervous system and reproductive system are still continuing to differentiate. When subjected to harmful drug effects, it may cause intrauterine growth retardation (FGR), low birth weight, functional behavioral abnormalities, and preterm delivery. Since improper use of drugs during pregnancy may cause serious consequences, the following principles of drug use should be followed: 1) the use of drugs must pay attention to the size of the gestational week, in the first three months of pregnancy should be cautious and prudent, can not be used or can be deactivated drugs should not be used or deactivated, available can not be used drugs should be used as much as possible, can be postponed to delay the treatment of delayed treatment, have to be used when possible to use the metabolism of the drug has a clear description of the drug should be used. 2) According to the different degree of influence the drugs may have on the fetus, choose the drugs that have the least influence on the fetus, and avoid the combined use of drugs if they can be used alone for treatment. 3) The dose and duration of the drug should be strictly controlled, the lowest effective dose should be used as much as possible, the duration of the drug should be as short as possible, and the effect on the newborn should be taken into consideration when the drug is used during delivery. 4) When the condition of pregnant women really need drugs that have an effect on the fetus, they should fully weigh the pros and cons and use them, adjust the dosage according to their condition and stop the drugs in time. In order to ensure the safety and reasonableness of the use of drugs during pregnancy, many countries have their own reference standards for the use of drugs and the evaluation of safe use of drugs during pregnancy, and the implementation of a grading system for the use of drugs during pregnancy. At present, the clinical use of western drugs in China refers to the U.S. FDA safety grading of drugs used during pregnancy. Based on the results of animal testing and clinical trials to evaluate the safety of drugs on the human body, the grading standards are: Class A: It has been confirmed that such drugs have no adverse effects on the human fetus. Only a very few drugs belong to this category, such as thyroxine, folic acid, vitamins, etc.; Grade B: animal experiments have proved harmless, but there is no sufficient evidence in humans. Most of the antibiotics commonly used in the clinic belong to class B drugs; Class C: animal experiments have proved harmful to animal embryos, but there is no relevant research in humans. For example, commonly used anti-tuberculosis drugs, this class of drugs can only be used when the benefits to the fetus outweigh the disadvantages; Class D: there is clear evidence of harm to the fetus. For example, aminoglycosides, tetracyclines, and high-dose vitamins. Despite the hazards, there is definitely a benefit to the pregnant woman when the drug is used, and may be considered when the pregnant woman has a serious illness or is threatened with death. Class X: Studies in animals or humans have shown that they can cause fetal abnormalities, and drugs in this class are contraindicated in patients who are or will be pregnant. For example, the antiviral drug triazole nucleoside. In the instructions of the drugs are listed in the drug classification, some drugs also have two different levels of risk, one is the level of common dose, the other is the level of abnormal dose, in the application of reference. The use of Chinese medicines during pregnancy also requires extra caution, the application of which is mainly based on China’s ancient medical knowledge of the dangers of using medicines during pregnancy, but the contraindications to pregnancy recorded in the important medical literature of the past generations, which varies from one literature to another. Mainly should be prohibited aconite, epiphyllum, croton, coriander, halberd, leeches, gadfly, centipede, andrographis, orpiment, petunia, musk and so on. Pre-pregnancy checkups and lifestyle modifications should be started in the third month before conception, which include avoiding CDX-rated drugs as much as possible.