The third week to the third month of pregnancy is the period of differentiation and formation of various organs of the embryo, which is easily affected by external factors such as drugs and other factors leading to fetal malformations, and belongs to the “highly sensitive period of teratogenicity”. The use of drugs at this time will have a greater impact on the development of the fetus, (especially drugs that are prohibited during pregnancy), but the chances and extent of the impact are different, and the type of drugs used, dose, duration and individual differences and other factors, is different from person to person. If you want to keep the baby, you can do pregnancy and childbirth examination (such as 14-20 weeks of pregnancy for Down’s syndrome screening, 22-26 weeks of pregnancy for ultrasound screening), and if necessary, amniocentesis, and any abnormalities will be treated promptly. Some pregnant moms may have heard that in the early stages of pregnancy (within 4 weeks from the first day of the last menstrual period), most medications have an “all or nothing” effect on the embryo, i.e., either they have no effect or cause a miscarriage, and generally do not result in fetal malformations. Who “gets away with it”? Yes, 99% of medications fall under the “all or nothing” theory and may not cause harm to the fetus. However, it should not be overlooked that there are a few exceptions to this theory. These include ribavirin, isotretinoin (formerly known as isotretinoin, a topical medication used to treat acne), and the prevention of measles, rubella, and other infectious diseases. and vaccines against measles, rubella, and mumps. Due to the long clearance half-life of these special drugs in the human body, the body to completely eliminate the drug from the body takes a long time, sometimes even months, at the same time, these drugs are clearly teratogenic, so not only pregnant mothers, even the preparation for pregnancy women should never be exposed to, and topical use is not allowed. Otherwise the drug residue in the body will increase the risk of fetal malformation.