Teratology is the study of abnormalities, malformations, monstrosities, and serious deviations from normal growth and development in organisms. The word teratogenesis is derived from the Greek gennan, meaning to produce, and terata, meaning monster. In humans, teratology is the study of chemicals, drugs, medications, alcohol, disease, or other environmental agents in relation to fetal abnormalities and birth defects. To be classified as a teratogen, an agent must cause either low birth weight, intrauterine growth retardation, or small size for gestational age; stillbirth or miscarriage; structural abnormalities; or functional defects (mental or developmental retardation). To cause birth defects, a teratogen must reach the developing fetus. Teratogens can also cause premature birth and fetal/newborn addiction to pharmacological agents. Thalidomide, tetracycline, valproic acid, cocaine, cigarette smoke, alcohol, lead, mercury, syphilis, herpes, and rubella are just a few examples of a teratogen.
Birth defects and abnormalities have baffled and frightened people throughout history: rock carvings and drawings from ancient civilizations around the world, including Australia and the Africas, depict individuals with deformities and malformations; writings from ancient Babylon describe them, as do clay tablets believed to date back to 2000 B.C. found in the library of an Assyrian king around 700 B.C.; and deformed human skeletal remains have been unearthed during archeological digs.
Before the advent of the modern study of birth defects in the 18th century, congenital abnormalities were viewed with superstition or as supernatural--perhaps punishment from the gods or the work of the devil. The first person to articulate the theory of "developmental arrest" was William Harvey in 1651 when he observed that a hair lip in a newborn infant closely resembled the normal condition of a fetus at a certain stage of development. Albrecht von Haller (1768) and Kaspar Friedrich Wolff (1759) followed a similar line of thinking. While not understanding the process, Ambroise Pare (1649) and John Hunter (1775) recognized familial and inherited traits. Gregor Johann Mendel began describing "inheritance laws," now known as genetics, in 1865; Carl Correns, Hugo de Vries, and Erich von Tschermak rediscovered this theory in 1900.
In spite of today's advanced medical and scientific knowledge, 3-5% of all infants are born with birth defects. Approximately 5% of those appear to be due to teratogens, a small percentage of which are preventable through pre-pregnancy counselling and the assessment of risk factors in certain populations. In many countries, educational and informational organizations are working toward reducing the number teratogen-related birth defects, while research continues investigating the phenomenon. For example, recent evidence indicates a woman can reduce her chances of bearing a child with spina bifida, one of the most common types of birth defects, by 50% simply by consuming at least 400 micrograms of folic acid (a B vitamin) daily for least one month prior to conception.
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