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Chapter 63 Reproductive Toxicology
Emese Zsiros, MD, PhD
❍ What are the FDA drug labeling categories for use during pregnancy?
The FDA-assigned five pregnancy categories as used in the Drug Formulary are as follows:
Category A: 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).
Category B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate
and well-controlled studies in pregnant women.
Category C: 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.
Category D: 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.
Category X: 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.
❍ What is the risk of birth defect in the general US population?
Every woman in the general population has a 3% risk of having a child with a birth defect. Birth defect is the
leading cause of infant mortality in the United States, accounting for 20.1% of all infant deaths.
❍ A 21-year-old female requests counseling because she was taking birth control pills without knowing she
was pregnant. What do you tell her?
Extensive epidemiologic studies have revealed no increased risk of birth defects in women who have used oral
contraceptives prior or during pregnancy. It is recommended for any patient who has missed her period that
pregnancy should be ruled out before continuing oral contraceptive use. Oral contraceptive use should be
discontinued if pregnancy is confirmed.