Drugs have been categorized by the Food and Drug Administration (FDA) according to the level of rishk to the fetus. Many of the medications included in this site refer to the Pregnancy Category. The following are descriptions of each category.
Controlled studies in women fail to demonstrate a risk to the fetus in the first trimester, and there is no evidence of risk in later trimesters; the possibility of fetal harm appears to be remote.
Either (1) animal reproductive studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or (2) animal reproductive studies have shown an adverse effect (other than decreased fertility) that was not confirmed in controlled studies on women in the first trimester and there is no evidence of risk in later trimesters.
Either: (1) studies in animals have revealed adverse effects on the fetus and there are no controlled studies in women or, (2) studies in women and animals are not available. Drugs in this category should be given only if the potential benefit justifies the risk to the fetus.
There is positive evidence of human fetal risk, but the benefits for pregnant women may be acceptable despite the risk, as in life-threatening diseases for which safer drugs cannot be used or are ineffective. An appropriate statement must appear in the "Warnings" section of the label of drugs in this category.
Studies in animals or humans have demonstrated fetal abnormalities, there is evidence of fetal risk based on human experience or both; the risk of using the drug in pregnant women clearly outweighs any possible benefit. The drug is contraindicated in women who are or may become pregnant. An appropriate statement must appear in the "Contraindications" section of the labeling of drugs in this category.