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Define Teratogen, and Give at Least Two Examples of Teratogens and Their Specific Effects

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Basically, a teratogen is an agent that, once in contact with a pregnant mother, will produce a defect in the developing fetus

A teratogen can be either a physical substance or a condition in the mother. The resulting defect can be either a physical abnormality or a functional defect. With this general definition in mind, it's obvious that types of teratogens and their resulting issues can run the gamut. After an egg is fertilized by a sperm, the resulting zygote travels to the uterus and develops into an embryo. Cells begin to divide, increasing the embryo's size, and it migrates from the fallopian tubes towards the uterus, where it eventually settles, implanting in the uterine wall. This does not occur until nearly a week after conception. After implantation, growth of supporting structures such as shared blood vessels begins. Finally, about 2-3 weeks after fertilization, the embryo shares a blood supply with the mother. It's around this time that the embryo can be affected by teratogens.

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Teratogens are substances that may produce physical or functional defects in the human embryo or fetus after the pregnant woman is exposed to the substance. Alcohol and cocaine are examples of such substances. Exposure to the teratogen affects the fetus or embryo in a variety of ways, such as the duration of exposure, the amount of teratogenic substance, and the stage of development the embryo or fetus is in during the exposure. Teratogens may affect the embryo or fetus in a number of ways, causing physical malformations, problems in the behavioral or emotional development of the child, and decreased intellectual quotient (IQ) in the child. Additionally, teratogens may also affect pregnancies and cause complications such as preterm labors, spontaneous abortions, or miscarriages. Teratogens are classified into four types: physical agents, metabolic conditions, infection, and finally, drugs and chemicals. The word teratogen originates from the Greek word for monster, teratos

Isidore Geoffroy Saint-Hilaire, a physician from Paris, France, defined it in 1832 in Histoire générale et particuliére des anomalies de l'organisation chez l'homme et les animaux (General and Particular History of Structural Monstrosities in Man and Animals). People had sought explanations for abnormal human and animal development, however, for centuries, and they had developed different theories about the causes for the abnormalities. In Babylon, many said that infants with congenital malformations, or structural abnormalities present at birth, were constellations in human forms as well as fortune-tellers. Many early Hebrews said that abnormal development resulted from the deformed person's association with the devil. Aristotle, who lived in Athens, Greece in the fourth century, B.C., deemed birth defects as disturbances in reproduction rather than supernatural occurrences. Aristotle and Hippocrates, a physician who practiced in Greece in the fifth century B.C., claimed that a pregnant woman's experiences or emotions, which became called maternal impressions, can affect the formation of the fetus. The theory of maternal impressions persisted until the early 1900s, despite evidence to the contrary by John Hunter, a surgeon in Scotland in the late eighteenth century. At the beginning of the 19th century, Johann Friedrich Meckel, the Younger, an anatomist from Halle, Germany, asserted that deviations from the normal developmental process caused malformations. Meckel wrote his doctoral thesis on an anatomical study of heart disease in 1802 and founded a journal dedicated to teratology, Journal für anatomische Varietäten, feinere und pathologische Anatomie (Journal of Anatomical Varieties, Finer and Pathological Anatomy).

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To summarize, premature and low birth-weight babies face an increased risk of serious health problems during the newborn period, chronic lifelong disabilities (e.g., cerebral palsy, mental retardation) and possibly death. More recent studies have suggested a possible link between prenatal smoking exposure and behavioral problems in later childhood and adolescence. In addition, almost three percent of pregnant women use illicit drugs such as marijuana, cocaine, Ecstasy and other amphetamines, and heroin

These drugs can cause low birth-weight, withdrawal symptoms, birth defects, or learning or behavioral problems.

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Sever LE, Mortenson ML: Teratology and the epidemiology of birth defects. In: Gabbe SG, Niebyl JR, Simpson JL (eds): Obstetrics: Normal and Problem Pregnancies. New York, Churchill-Livingstone, 185–214, 1996

Wilson JG, Fraser FC (eds): Handbook of Teratology. New York, Plenum, 1979

Teratology Society Public Affairs Committee. FDA Classification of drugs for teratogenic risk Teratol 49:446, 1994

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