These
definitions are those used by the United States Food and Drug
Administration (FDA).
These
categories do not imply an increasing progression of risk from A to
X. Drugs are categorized based on the risk of reproductive and
developmental adverse effects and on risk versus benefit
considerations. Drugs in categories D, X and is some cases C, may
pose similar risk, but may be categorized differently on the basis of
different risk versus benefit considerations.
FDA Use-In-Pregnancy Ratings
Category A
- Adequate, well-controlled studies in pregnant women have not shown an increased risk of fetal abnormalities to the fetus in any trimester of pregnancy.
- Controlled studies in women fail to demonstrate a fetal in the first trimester (and there is no evidence of a risk in later trimesters), and the possibility of fetal ham remains remote.
Category B
- Animal studies have revealed no evidence of harm to the fetus, however, 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 in any trimesters.
- Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).
Category C
- Animal studies have shown an adverse effect and there are no adequate and well-controlled studies in pregnant women; or no animal studies have been conducted and there are no adequate and well-controlled studies in pregnant women.
- Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.
Category D
- Adequate well-controlled or observational studies in pregnant women have demonstrated a risk to the fetus. However, the benefits of therapy may outweigh the potential risk. For example, the drug may be acceptable if needed in a life-threatening situation or serious disease for which safer drugs cannot be used or are ineffective.
- There is positive evidence of human fetal risk, but the benefit from use in pregnant women may be acceptable despite the risk
Category X
- Adequate well-controlled or observational studies in animals or pregnant women have demonstrated positive evidence of fetal abnormalities or risks. The use of the drug is contraindicated in women who are or may become pregnant.
- Studies in animals or human beings have demonstrated fetal abnormalities or there is evidence of fetal risk based on human experience or both, and the risk of the use of the drug in pregnant women clearly outweighs any possible benefit.
