Every family wants to have a healthy and smart baby, and more and more mothers-to-be are becoming concerned about the safety of medication during pregnancy. Improper medication during pregnancy can affect the fetus, the most serious being drug toxicity that affects embryonic differentiation and development, leading to fetal malformations and dysfunction. Therefore, mothers-to-be should be cautious in taking medication throughout pregnancy. The effect of drugs on the fetus depends on the developmental stage of the fetus at the time of drug use and can be broadly divided into the following periods: 1. Pre-pregnancy: Before the fertilization of the egg, during this period, the use of drugs is generally safe. However, it is important to pay attention to the half-life of the drug, as drugs with a long half-life may affect the growth of the embryo. 2. From fertilization to the end of the fourth week of pregnancy: The effect of drugs on the embryo during this period is “all” or “none”. “All” means that the drug causes damage to a large number of embryonic blastocyst cells, resulting in the death of the embryo and its natural elimination before implantation. “None” means that the drug only damages a small number of cells and does not affect other blastocyst cells that continue to differentiate and develop into normal individuals. Therefore, this period is a safe period for the use of drugs. 3.Fertilization from the 15th month to about 3 months of gestation: This period is the classic teratogenic period. Since various important organs, trunk and limbs differentiate rapidly within this short period of time, they are extremely vulnerable to various teratogenic factors including drug toxicity. Once the organs that are differentiating are affected, malformations may be formed. The earlier the toxic effect of drugs in this period, the more serious the malformation may occur. 4.3 months of gestation to delivery: The fetus has completed the differentiation of major organs and continues to develop and grow, but the nervous system and reproductive system continue to differentiate, some drugs may affect the normal development of the fetus, resulting in intrauterine growth retardation, low birth weight, abnormal functional behavior and premature birth. Therefore, the use of drugs during pregnancy should pay attention to the size of the gestational week, and try not to use or stop using drugs during the third month of pregnancy. When drugs must be used during pregnancy, you should try to choose the drug that has the least impact on the fetus after fully weighing the pros and cons, and adjust the dosage of drugs according to the condition at any time and stop the drugs in time.