Any agent (e.g., alcohol, rubella) or environmental influence (e.g., exposure to X-rays, PCBs) that results in the abnormal development of the growing fetes, particularly non-heritable birth defects. The abnormalities consist of two outcomes: congenital malformations and congenital anomalies. Teratogenic effects can result in damage to organiser capacity of cells or their competence to react to organisers, an altered rate of cell proliferation, interference with cell migration, failure of cells to aggregate, and the prevention of the synthesis of enzymes. There are two general stages of teratogenic susceptibility during the embryonic period in humans. The first weeks when leading to perinatal death or complete regeneration, and 3-10 weeks resulting in congenital malformations in major anatomical structures such as the heart, ears and eyes. A third stage, after 10 weeks, is associated with congenital anomalies, particularly in the developing brain. Teratogens exert their effects during what appear to be sensitive periods for the growth of particular body parts.
See Alcohol tolerance, Carcinogen, Congenital anomalies, Congenital abnormalities, Enzymes, Fetal alcohol syndrome (FAS), Methyl mercury, Miniamata disease, Mutagens, Retinoic acid, Sensitive period, Thalidomide, TORCH