Outpatient clinics and online medical platforms often encounter expectant mothers who are worried and anxious about the history of medication use and consult the baby to stay or go. Today, we have a science on this issue. The extent to which the use of medication in pregnant women can damage the baby is closely related to the number of weeks of pregnancy when the medication is used, in addition to the composition of the medication. Within two weeks after conception, the fertilized egg is still in the fallopian tube or uterine cavity and has not yet come into direct contact with the mother’s tissue, so the effect of the drug on the embryo is not significant; if the drug is extremely toxic to the blastocyst, it will kill the embryo and cause a spontaneous abortion. At this time, the effect of the drug can be described as “all or nothing”, which means that the embryo dies early and leads to miscarriage; nothing means that the embryo continues to develop without any abnormality. The fetal organs are highly differentiated, rapidly developing and forming stage, any part of the cells are affected by cytotoxicity, may cause malformation, so the sensitivity of the fetus to drugs at this stage is extremely high, also called “tissue and organ hypersensitivity period”, the use of drugs at this time should be particularly cautious. In the first 13 weeks of pregnancy, it is better not to use drugs of grade C, D or X. If a pregnant woman has to use drugs in case of emergency, she should try to use drugs of grade A or B under the guidance of her doctor. After the 13th week of pregnancy, most of the organs of the embryo have been formed and the fetus is less sensitive to drugs, however, the brain and the genitourinary system continue to differentiate at this time and will still be more sensitive to drugs. The nervous system continues to differentiate and develop throughout pregnancy, so the effects of drugs on the nervous system will continue to exist, and caution is still needed when using drugs at this time.