FDA Pregnancy Categories

A:  Adequate and well-controlled studies in pregnant women have failed to show a risk to the fetus in the first trimester of pregnancy and there is no evidence of risk in later trimesters.

B:  Animal studies have failed to show a risk to the fetus and there are no adequate and well-controlled studies in pregnant women; or animal studies have shown an adverse effect but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the fetus during the first trimester of pregnancy and there is no evidence of a risk in later trimesters.

C:  Animal studies have shown an adverse effect on the fetus, there are no adequate and well-controlled studies in humans, and the potential benefits may outweigh the risks; or there are no animal studies and no adequate and well-controlled studies in humans.

D:  Positive evidence of human fetal risk but the benefits may outweigh the risks.

X:  Animal or human studies have shown fetal abnormalities or toxicity, or both, and the risks clearly outweigh any possible benefits.