Maternal illnesses can threaten the embryo and fetus, while maternal drug treatment can lead to early recovery of the disease and facilitate the growth and development of the embryo and fetus. Drugs are dual in nature. The proper use of medication can cure the disease, but the improper use of medication can bring harm. The use of drugs for maternal illness must not only have no significant adverse effects on the mother, but also must ensure that there are no adverse effects on the embryo, fetus and the newborn born. Some drugs do have adverse effects on the embryo and fetus, and the extent of such effects is closely related to the gestational age of the fetus at the time of administration. It is evident that obstetric drugs should be used with the safety of the mother and child as the first priority and should be used rationally. The U.S. Food and Drug Administration (FDA) classifies drugs into five classes: A, B, C, D, and X, according to their teratogenicity to the fetus. Class A drugs: Controlled studies have shown no harm. It has been confirmed that such drugs have no adverse effects on human and fetus, and are the safest; Class B drugs: no evidence of harm in human or animal experiments are not harmful to fetal animals, but there are no adequate studies in humans: Class C drugs: harm cannot be excluded, animal experiments may be harmful to fetal animals or lack of studies, there are no relevant studies in humans. This class of drugs should be used only after weighing the benefits to the pregnant woman against the harms to the fetus; Class D drugs: there is clear evidence of harm to the fetus. Despite the risk, there is an absolute benefit to the pregnant woman, and may be considered if the pregnant woman has a serious illness or is threatened with death and needs the drug urgently; Class X drugs: Studies in either animals or humans have shown that they can cause fetal abnormalities or are empirically considered harmful in humans, or in both humans and animals. Drugs in this class are contraindicated in patients who are or will be pregnant. Chinese herbal medicines or proprietary Chinese medicines are generally indicated as “caution” or “prohibited” for pregnant women. The principles of maternal medication are: avoid combined medication if you can use a drug; avoid new drugs that are difficult to determine without adverse effects on the fetus if you can use an old drug with positive efficacy; avoid large doses of drugs if you can use small doses.