2. An environmental agent that can cause abnormalities in a developing organism resulting in either fetal death or congenital abnormality.
Normally a human fetus is separated from the mother by the placental barrier, but if the barrier is imperfect and permits a number of chemical and infectious agents to pass to the fetus, then abnormalities may result.
2. Any agent that can disturb the development of an embryo or fetus.
Teratogens may cause a birth defect in the child or it may halt the pregnancy outright. The classes of teratogens include radiation, maternal infections, chemicals, and drugs.