Teratogens

A teratogen is an environmental agent that can adversely affect the unborn child, thus producing a birth defect. Teratogens include infectious agents, such as rubella, syphilis, and herpes, and chemicals. Chemical exposures can occur through lifestyle choices (e.g., alcohol, smoking, drugs) or exposure to environmental hazards (e.g., X rays, certain environmental chemicals). The teratogenicity, or nature and extent of harm to the fetus, is influenced by fetal genetic vulnerability, type and amount of teratogen, and timing of the exposure during pregnancy. For example, certain teratogens may have adverse effects only during critical periods of fetal development or after a certain amount of exposure. There are possible exceptions to these principles in which teratogenic exposures may not result in negative effects. There are also agents and conditions with possible, but unproven, effects on fetuses. Therefore, it is important to check with a knowledgeable source for possible consequences of exposure.