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...