FDA Pregnancy Risk Categories Prior to 2015
In 1979, the FDA established five letter risk categories - A, B, C, D or X - to indicate the potential of a drug to cause birth defects if used during pregnancy. The categories were determined by assessing the reliability of documentation and the risk to benefit ratio. These categories did not take into account any risks from pharmaceutical agents or their metabolites in breast milk. In the drug product label, this information was found in the section “Use in Specific Populations”.
The former pregnancy categories, which still may be found in some package inserts, were as follows:
Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).
Example drugs or substances: levothyroxine, folic acid, liothyronine
Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.
Example drugs: metformin, hydrochlorothiazide, cyclobenzaprine, amoxicillin, pantoprazole
Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
Example drugs: tramadol, gabapentin, amlodipine, trazodone
There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
Example drugs: lisinopril, alprazolam, losartan, clonazepam, lorazepam
Studies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience, and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits.
Example drugs: atorvastatin, simvastatin, warfarin, methotrexate, finasteride