Teratogens: Identifying

How do scientists identify teragogens?

Scientists conduct animal studies or rely on observation to determine if a substance is a teratogen.

• Animal studies - Animal studies are the primary way a medication is determined to be safe for humans. It's important to keep in mind, however, that a drug does not always affect an animal the same way it will affect a human.
• Observations from human exposure - In the past, there have been medications that caused birth defects. One example is thalidomide, which was removed from the market in the 1960s when it was found to cause babies to be born with missing and malformed limbs to mothers who took the drug early in pregnancy.

How are medications rated for their safety?

Before 1980, most medications included literature that stated that their use in pregnancy had not been approved. Since that time, the US Food and Drug Administration (FDA) has created five drug categories to designate the safety of medications for their use during pregnancy, with A being the safest and X being the most dangerous.

The categories are as follows:

• Category A - Carefully controlled studies have failed to show any risk to a fetus in the first trimester of pregnancy and there is no evidence of any risk in later trimesters. An example would be prenatal vitamins in recommended dosages.
• Category B - Studies in pregnant animals have failed to show a risk to the fetus but there are no well-controlled studies in pregnant women.
• Category C - Animal studies have shown that there is a risk to the fetus; however, there may be potential benefits to the mother that outweigh the risks.
• Category D - There is evidence that a drug will harm a developing fetus but the potential benefits may warrant using the drug despite the potential risk.
• Category X - Studies in animals or humans show the drug leads to fetal abnormalities and the risks involved in using the drug in pregnant women clearly outweigh any potential benefits.