The U.S. Drug and Food Administration (FDA) classifies the effects of drugs on pregnancy into five classes, depending on the degree of teratogenicity of the drug in animals or humans: I. Adequate well-controlled studies of pregnant women in the first trimester have found no fetal harm (and no evidence of harm in the subsequent 6 months). The effect of these drugs on the fetus is minimal. There are very few drugs of class A. Vitamins fall into this category, such as various vitamins B and C. However, vitamin A in normal range doses is a class A drug, while large doses of vitamin A, 20,000 IU per day, can be teratogenic and become a class X drug. Second, animal studies did not find any harm to the fetus, but there is no adequate well-controlled study in pregnant women; or animal studies found harm to the fetus, but adequate well-controlled study in pregnant women did not find any harm to the fetus. These drugs have less effect on the fetus. There are not many drugs in Class B, but happily, all of the antibiotics used daily are in this category. For example, all the penicillins and most of the cephalosporins are class B drugs, and the commonly used ampicillin, cefradine, ceftazidime and ceftazidime are all class B drugs. In addition, Zithromax, Clindamycin, Erythromycin, Furantoin and Metronidazole are also class B drugs. Among the commonly used antipyretic and analgesic drugs, indomethacin (anti-inflammatory pain), diclofenac (furosemide) and ibuprofen (fenpropathrin) are all class B drugs. Animal studies have shown that the drugs have teratogenic or embryonic killing effects on fetuses, but there are no adequate well-controlled studies on pregnant women; or there are no studies on pregnant women and no animal studies. Such drugs must be evaluated by a physician and weighed against the pros and cons before use. In the antibiotic class of quinolones, for example, this class of drugs in animal experiments found thatloxacin has damage to cartilage, in humans there have been reports of more than 6 0 0 cases of early pregnancy taking the drug, after the birth of children in the growth period of 6 cases have leg and other pain, but soon after the symptoms disappeared, none left sequelae, so the argument of the data, the drug is still safe. However, the clinic still has to wait for more reports to confirm its harmlessness. Caution should be exercised in the use of Class C drugs. If an alternative drug is available, choose the alternative drug; otherwise, after weighing the pros and cons, explain to the patient or the patient’s family the reasons for choosing the drug. The antiepileptic drugs levetiracetam, lamotrigine, oxcarbazepine, and topiramate are Class C. IV. There is clear evidence of harm to the human fetus, but in some cases (e.g., where there is a serious, life-threatening illness in the pregnant woman and no safer drug is available, or where the drug is safe but ineffective for use) the benefits of using the drug in pregnant women outweigh the harms. The tetracyclines are typical among antibiotics. The use of tetracycline or hyoscine during pregnancy destroys fetal tooth enamel and results in yellowing of teeth by adulthood. Aminoglycosides are not used during pregnancy as much as possible, such as streptomycin, which may damage the eighth pair of cranial nerves and cause hearing loss. As for antineoplastic drugs, they are almost all class D drugs. Among the central nervous system drugs, analgesics are class B drugs when used in small doses, and class D drugs when used in large doses, which are harmful to the fetus, especially when applied for a long time, mainly due to poor fetal growth and development and addiction to drugs after delivery, irritability, crying, etc. Many of the antiepileptic drugs are class D drugs, such as primidone, trimethadione, etc., have teratogenic effects, and it should be noted that the rate of fetal malformation after pregnancy is higher in patients with epilepsy than in the general population. The use of antiepileptic drugs can increase the rate of fetal malformations, especially when several antiepileptic drugs are used together to increase the rate of fetal malformations. Phenobarbital, sodium phenytoin, carbamazepine, sodium valproate, and clonidine are Class D drugs. Among the sedative and hypnotic drugs, diazepam, chlordiazepoxide, meprobamate and norethindrone are all class D. If a pregnant woman has early pregnancy reaction and insomnia in early pregnancy, she cannot be given these drugs. V. Animal or human studies have shown that they can cause fetal abnormalities; or there is clear evidence of harm to the fetus based on human and animal experience with medication. There is clearly no benefit to the use of drugs in pregnant women. Contraindicated in women who are or may become pregnant. The best known of these is phthalazinone (reactive stop), which was taken in the late 1950s and early 1960s by women near allied sites in Europe to reduce pregnancy reactions, and was later found to cause a number of fetuses to be born with short upper limbs and combined lower limbs in a seal-like shape, hence the term seal-like deformity, which was recognized earlier as a class X drug. The common drugs are mifepristone, clomiphene, ribavirin (virazole).