Introduction of an agent (chemical substance, virus, or ionizing radiation) that when administered prenatally to the mother can cause malformations of an embryo or fetus (birth defects).
Teratogenesis is a medical term from the Greek, literally meaning monster-birth, which derives from teratology, the study of the frequency, causation, and development of congenital malformations—misleadingly called birth defects. These include gross morphological abnormalities, such as cleft lip and/or palate, anencephaly, or ventricular septal defect, but may also include phenomena such as increased risk of cervical cancer or discoloration of tooth enamel. These malformations can arise from genetic abnormalities of the fetus, from adverse environmental circumstances (termed teratogens or tetragens), or a combination of these factors.