Teratology is the study of abnormalities, malformations, monstrosities, and serious deviations from normal growth and development in organisms. The word teratogenesis is derived from the Greek gennan, meaning to produce, and terata, meaning monster. In humans, teratology is the study of chemicals, drugs, medications, alcohol, disease, or other environmental agents in relation to fetal abnormalities and birth defects. To be classified as a teratogen, an agent must cause either low birth weight, intrauterine growth retardation, or small size for gestational age; stillbirth or miscarriage; structural abnormalities; or functional defects (mental or developmental retardation). To cause birth defects, a teratogen must reach the developing fetus. Teratogens can also cause premature birth and fetal/newborn addiction to pharmacological agents. Thalidomide, tetracycline, valproic acid, cocaine, cigarette smoke, alcohol, lead, mercury, syphilis, herpes, and rubella are just a few examples of a teratogen.

Birth defects and abnormalities have baffled and frightened people...