Women with unintended pregnancies who are exposed to teratogens constitute the highest risk group for fetal harm. Teratogen exposures come from substances, medications, chronic and acute diseases, and environmental factors. Nurses play a critical role In reducing unintended pregnancy and promoting preconception health. A greater understanding of the role of teratogens and strategies to improve history taking and help women prevent unintended pregnancy will improve nurses' ability to reduce teratogen exposure in women at risk.