Teratogen means, in Greek, "monster forming." Teratogens are chemicals that cause abnormalities in embryos. The most well-known is thalidomide, a drug originally designed to combat morning sickness in pregnant women. It caused the long bones in the arms or legs of fetuses to not develop properly, resulting in babies with severely stunted arms or legs.
Teratogen is a type of mutagen that causes mutations in somatic cells (cells that are not part of the reproductive system). Mutagens induce mutations of deoxyribonucleic acid ( DNA ), the hereditary material in cells. The damage of DNA may either kill the cells or, when misrepaired, produce abnormal sequences that will be passed on to daughter cells. This may result in birth defects by injuring developing organs or by disorganizing growth and differentiation.
Apart from thalidomide, the steroid hormones have also been identified as teratogens. The use of male sex hormones as a treatment for breast cancer has resulted in the masculinization of a number of female fetuses when such treatment was commenced prior to the twelfth week of gestation. In addition, the accepted practice of using progesterone from natural sources for the treatment of miscarriage led to the widespread use of synthetic hormones between 1950 and 1960. The result was the birth of more than 600 female babies with equivocal or frankly masculinized external genitalia. It
was found later that these synthetic compounds had appreciable androgenic (related to the male sex hormone) activity.
There are other chemicals suspected of being teratogenic because they are occasionally associated with malformations in the offspring of women treated during pregnancy. These include anticonvulsants and some oral hypoglycemics when taken at high doses during pregnancy. It is, however, very difficult to determine the teratogenesis of a drug. Long and costly surveys must be done on a very large population to associate a particular drug with birth defects.
Wilson, James G. (1973). "Present Status of Drugs as Teratogens in Man." Teratology: International Journal of Abnormal Development 7: 3–15.
"OTIS Fact Sheets." Organization of Teratology Information Services. Available from http://www.otispregnancy.org .