From the Guidelines
The FDA pregnancy categories (A, B, C, D, and X) classify medications based on their potential risk to the developing fetus, with Category A being the safest and Category X being contraindicated during pregnancy due to high fetal risk. The categories are defined as follows:
- Category A: Adequate, well-controlled studies in pregnant women have not demonstrated a risk to the fetus in any trimester.
- Category B: Animal reproduction studies have not demonstrated a fetal risk, but there are no adequate, well-controlled studies in pregnant women, or animal studies have shown an adverse effect that was not confirmed in controlled studies in women.
- Category C: Animal studies have shown an adverse effect on the fetus, but there are no adequate, well-controlled studies in women, or studies in women and animals are not available.
- Category D: There is evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk.
- Category X: Studies in animals or human beings have demonstrated fetal abnormalities, or there is evidence of fetal risk based on human experience, and the risk of the use of the drug in pregnant women clearly outweighs any possible benefit. Examples of medications and their respective categories include isotretinoin (Category X), warfarin (Category D), amoxicillin (Category B), and folic acid (Category A) 1. It's essential to note that in 2015, the FDA replaced this lettering system with more descriptive pregnancy risk information, but many healthcare providers still reference the original categories when discussing medication safety during pregnancy 1. Any medication use during pregnancy should always be discussed with a healthcare provider to weigh individual risks and benefits.
From the Research
Drug Categories and Safety Profiles
The categories of drugs, referred to as ABCD, etc., pertain to their safety profiles during pregnancy. These categories are used to classify drugs based on their potential risks to the fetus.
- Category A: Includes drugs that have been extensively used and/or for which there are reliable clinical data indicating no evidence of disturbance of the reproductive process 2.
- Category B: Includes drugs for which data from pregnant women are insufficient for making any solid estimation of human teratogenic risk, and classification is therefore based on animal data 2.
- Category C: Includes drugs for which the pharmacological action of the drug may have undesirable effects on the human fetus or newborn infant 2.
- Category D: Contains drugs for which human data indicate an increased incidence of malformations 2.
- Category X: Includes drugs with potential teratogenic risk that outweighs maternal benefit 3.
Classification Systems
There are different classification systems used to categorize drugs based on their safety profiles during pregnancy, including the Swedish system and the US Food and Drug Administration (FDA) system. These systems have different definitions and allocation of drugs to categories, resulting in varying classifications for the same drug 2.
Medication Safety in Pregnancy
Medication use in pregnancy is common, but information about the safety of most medications in pregnant women or their infants is limited 4. Studies have shown that many medications are prescribed during pregnancy, and the frequency and type of medications prescribed can vary depending on the stage of pregnancy 3. It is essential to have accurate and reliable information about the safety of medications during pregnancy to inform decision-making by regulators, clinicians, and patients.