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Table 2 Categories of risk for drugs during pregnancy [38]

From: Translational toxicology: a developmental focus for integrated research strategies

Category Description
A These drugs are the safest. Well-designed studies in people show no risks to the fetus.
B Studies in animals show no risk to the fetus, and no well-designed studies in people have been done.
Studies in animals show a risk to the fetus, but well-designed studies in people do not.
C No adequate studies in animals or people have been done.
D Evidence shows a risk to the human fetus, but benefits of the drug may outweigh risks in certain situations. For example, the mother may have a life-threatening disorder or a serious disorder that cannot be treated with safer drugs.
X Risk to the fetus has been proved to outweigh any possible benefit.