The FDA has assigned a pregnancy risk category to each systemically absorbed drug based on available clinical and preclinical information. The five categories (A, B, C, D, and X) reflect a drug’s potential to cause birth defects. Although drugs are best avoided during pregnancy, this rating system permits rapid assessment of the risk-benefit ratio should drug administration to a pregnant woman become necessary. Drugs in category A are generally considered safe to use in pregnancy; drugs in category X are generally contraindicated.
Pregnancy Category A Adequate studies in pregnant women have failed to show a risk to the fetus.
Pregnancy Category B Animal studies haven’t shown a risk to the fetus, but controlled studies haven’t been conducted in pregnant women; or animal studies have shown an adverse effect on the fetus, but adequate studies in pregnant women haven’t shown a risk to the fetus.
Pregnancy Category C Animal studies have shown an adverse effect on the fetus, but adequate studies haven’t been conducted in humans. The benefits from use in pregnant women may be acceptable despite potential risks.
Pregnancy Category D The drug may cause risk to the fetus, but the potential benefits of use in pregnant women may be acceptable despite the risks (such as in a life-threatening situation or a serious disease for which safer drugs can’t be used or are ineffective) .
Pregnancy Category X Studies in animals or humans show fetal abnormalities, or adverse reaction reports indicate evidence of fetal risk. The risks involved clearly outweigh potential benefits.