Teratogen
A teratogen is a substance that can cause physical malformations if a fetus or embryo is exposed to that substance while in the mother's womb. Scientists group teratogens with mutagens and carcinogens because all three cause mutations (changes) in the fetus or embryo. The three terms share the root "gen" which means birth or origin. While a teratogen causes physical changes, a carcinogen causes cancer, and mutagen causes genetic changes. In other words, it changes the genes within a cell of a fetus.
When a fetus is exposed to a teratogen, results vary:(1)a low dose or exposure during a non-critical time of development of the fetus may result in no effect;(2)severe malformations may cause the fetus to die and the pregnancy will result in a miscarriage; or (3)the baby may be born with birth defects.
Birth defects are a significant concern to our society because they occur in 3-5% of newborns. Birth defects may include growth retardation (slow growth), mental retardation, structural defects (such as a missing or malformed limb), or functional damage. An example of functional damage is the effect of a drug called diethystilbestrl (DES). Female babies who were exposed to DES while in their mother's womb have suffered damage to their reproductive systems. As adults, the daughters who were exposed to DES while in their mother's womb have had trouble in becoming pregnant and have suffered unusually high rates of miscarriage.
Substances that can cause birth defects include viral diseases, physical agents, and chemicals. For example, rubella (German measles) is caused by a virus. If a mother becomes infected during pregnancy, the virus causes birth defects. Radiation is physical agent that causes birth defects. Exposure to radiation can occur naturally in the environment or through sources controlled by humans such as x-rays. A few chemicals are known to be teratogenic in humans. They include anti-cancer drugs, steroid hormones, and an infamous drug called thalidomide. Thalidomide was used in Europe in the 1960s to relieve nausea during pregnancy. However, it resulted in horrible defects in the mothers' babies. Thousands of babies were born with malformed or missing arms, legs, or both. The thalidomide disaster brought worldwide attention to the fact that the mother's womb does not protect the fetus from the effects of drugs. Today, many chemicals including many prescription drugs are suspected to be teratogens even if definite proof is unavailable. Therefore, pregnant mothers are usually advised to avoid all unnecessary drugs during pregnancy, especially during the first three months.
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