In 2016 the FDA (Food and Drug Administration) removed the old pregnancy categories A, B, C, D, or X, with new descriptions, the Pregnancy and Lactation Labeling Rule (PLLR). The new recommendations in the form of drug labeling have increased details and complexity. New package inserts will now contain individualized narrative summaries for each medication that includes the “risks of using a drug during pregnancy and lactation, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy and lactation.”

New PLLR subsections

The new subsections are:

1. Pregnancy (Labor & Delivery) 
2. Lactation (Nursing Mothers)
3. Females & Males of Reproductive Potential

The old pregnancy drug categories until 2016

Category A: Adequate studies inpregnant women have not demonstrated 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 remote. Example: Vitamin C, when used in recommended daily allowance dosage

Category B: Animal studies have not demonstrated fetal risk but there are no adequate studies in pregnant women, or animal studies have shown an adverse effect (other than a decrease in fertility), but adequate studies in pregnant women have not demonstrated a risk to the fetus during the first trimester and there is no evidence of risk in later trimesters). Example: Ampicillin.

Category C: Animal studies have shown an adverse effect on the fetus (teratogenic, embryocidal, or other) but there are no adequate studies in humans. The benefits from the use of the drug in pregnant women may be acceptable despite its potential risks, or there are no animal reproduction studies and no adequate studies in humans. Example: Zidovudine (AZT).

Category D: Positive evidence of human fetal risk exists, but the potential benefits from the use of the drug in pregnant women may be acceptable despite these risks (for a life-threatening condition or a serious disease for which safer drugs cannot be used or are ineffective). Example: Phenytoin (anticonvulsive).

Category X: Studies in animals or humans demonstrate fetal abnormalities or adverse-reaction reports indicate evidence of fetal risk. The risk of use in a pregnant woman clearly outweighs any possible benefit. Example: Isotretinoin