FDA Pregnancy Categories
Category A
Adequate studies in pregnant women have failed to show a risk to the fetus in the first trimester and there is no evidence of risk in later trimesters.
Category B
Animal studies have failed to show a risk to the fetus but there are no adequate studies in pregnant women: or animal studies have shown an adverse effect but human studies have not shown a risk to the fetus in the first trimester and there is no evidence of risk in later trimesters.
Category C
Animal studies have shown an adverse effect on the fetus but there are no adequate studies in humans, but the benefits may outweigh the risks; or there are no aminal studies and no adequate human studies.
Category D
Positive evidence of human fetal risk but the benefits may outweigh the risks.
Category X
Animal or human studies have shown fetal abnormalities or toxicity, and the risk outweighs the benefits.