The U.S. Food and Drug Administration (FDA) reports the risk of drugs to the fetus and classifies drugs in pregnancy into the following five classes: Class A – In controlled drug studies, no evidence of fetal harm was seen in women in the first trimester (and no evidence of harm in the next 6 months). This class of drugs has been shown to have no adverse effects on the fetus and is the safest class. Class B – No adverse effects of the drug on the fetus have been seen in animal studies. Grade B – No proven adverse effects on the fetus in animal studies and in humans, and animal studies indicating no harm to fetal animals, but no adequate studies in humans have been reported. Class C – Animal studies have demonstrated that the drug is harmful to the fetus (teratogenic or fetal death, etc.), or there are no studies in pregnant women with controls, or no studies have been conducted on pregnant women and animals. This class of drugs should only be used after weighing the benefits to the pregnant woman against the risks to the fetus; Class C is not adequately studied in animals and humans; or there are adverse effects on animals and fetuses, but no observations on humans have been reported. This class of drugs is the most difficult to choose clinically. Class D – Drugs with clear evidence of harm to the human fetus, but nevertheless of absolute benefit to the pregnant woman (e.g., using the drug to save her life or to treat a serious illness for which other safer drugs are ineffective); Class D is drugs that show signs of harm to the fetus, but the benefits of treating the pregnant woman’s illness clearly outweigh these harms, such as the antiepileptic phenytoin sodium. Class X – Drugs that have been shown to be harmful to the fetus in animal and human studies or experience with human medications and are contraindicated in patients who are pregnant or may become pregnant because of the lack of benefit from their use in pregnant women. class X is drugs that have been shown to be harmful to the fetus and are contraindicated during pregnancy.