The term "Pregnancy Risk Factor" followed by letter A, B, C, D or X signifies a pregnancy category. The FDA established these five categories to indicate the potential of a systemically absorbed drug for causing birth defects. The categories are determined by the reliability of documentation and the risk to benefit (risk:benefit) ratio.
Pregnancy category X is particularly distinguished in that if any data exists that may implicate a drug as a teratogen (potentially causing birth defects) and the risk to benefit ratio is clearly negative, the drug is contraindicated (prohibited from use) during pregnancy.
Sometimes a drug taken by a woman during pregnancy may enter a fetus, causing damage or birth defects. The risk of damage done to a fetus is the greatest in the first few weeks of pregnancy, when major organs are developing. However, researchers do not know if taking medicines during pregnancy may also have negative effects on the baby later on.
Introduced in 1979, the pregnancy category of a pharmaceutical agent is an assessment of the risk of fetal injury due to the pharmaceutical, if it is used as directed by the mother during pregnancy. It does not include any risks given by pharmaceutical agents or their metabolites that are present in breast milk.
The FDA requires a relatively large amount of high-quality data on a pharmaceutical for it to be defined as pregnancy category A. As a result of this, many drugs that would be considered pregnancy category A in other countries are allocated to category C by the FDA.
Birth defects, category A, category B, category C, category D, category X, fetal development, pregnancy risk factor, teratogen.
Category A: Controlled studies in pregnant women fail to demonstrate a risk to the fetus in the first trimester with no evidence of risk in later trimesters. The possibility of fetal harm appears unlikely. Examples may include: folic acid, vitamin B6 and thyroid medicine in moderation or in prescribed doses.
Category B: 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. Examples may include: some antibiotics, acetaminophen (Tylenol), aspartame (artificial sweetener), famotidine (Pepcid), prednisone (cortisone), insulin (for diabetes), and ibuprofin (Advil, Motrin) before the third trimester. Pregnant women should not take ibuprofen during the last three months of pregnancy.
Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal effects 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 benefits justify the potential risk to the fetus. These drugs may include prochlorperazine (Compazine), Sudafed, fluconazole (Diflucan) and ciprofloxacin (Cipro). Some antidepressants are also included in this group.
Category D: There is positive evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g. if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective). Examples may include alcohol, lithium (used to treat manic depression), phenytoin (Dilantin) and most chemotherapy drugs to treat cancer. In some cases, chemotherapy drugs may be given during pregnancy.
Category X: 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. The drug is contraindicated in women who are or may become pregnant. Examples may include: drugs to treat skin conditions like cystic acne (Accutane) and psoriasis (Tegison or Soriatane); a sedative (thalidomide); and a drug to prevent miscarriage used up until 1971 in the United States and 1983 in Europe (diethylstilbestrol or DES).