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Teratogens are drugs, chemicals, or even infections that can cause abnormal fetal development. There are billions of potential teratogens, but only a few agents are proven to have teratogenic effects.


There are some organ systems that are sensitive to teratogens throughout the entire pregnancy, such as the central nervous system. The central nervous system is the baby's brain and spine. One teratogen that affects the central nervous system is alcohol.


Examples of Teratogens. There are many different examples of teratogens that cause birth defects. Listed in the directory below are some, for which we have provided a brief overview. Fetal Alcohol Syndrome (FAS) Phenytoin (Dilantin) Varicella


Effects of teratogens during this period of developmental often times results in an “all or none effect.” That is, the effect of the teratogen, if it is to have any effect, will be so profound as to cause a spontaneous abortion. Some examples of teratogens known to cause human malformations are listed in the table below (Table 23-2).


Some teratogens may have delayed effects, and these do not result in an overt congenital malformation; diethylstilbestrol (DES) exposure in a female fetus can predispose to vaginal clear cell carcinoma in puberty.. Embryogenesis. The developmental timing of the event that results in the final phenotype is one of the critical determinants of the phenotypic outcome.


The four most common teratogens are tobacco, alcohol, medications and illegal drugs. Teratogens are substances that could harm a developing fetus by affecting growth and causing birth defects or death. The use of tobacco during pregnancy is dangerous because the smoke causes the blood vessels to constrict.


Teratogen: Any agent that can disturb the development of an embryo or fetus. Teratogens may cause a birth defect in the child. Or a teratogen may halt the pregnancy outright. The classes of teratogens include radiation, maternal infections, chemicals, and drugs.


à some teratogens cause damage only during specific days or weeks in early pregnancy. à other teratogens are harmful at any time during the pregnancy---for example, for behavioral teratogens, there is no safe period---the brain and nervous system can be harmed throughout the pregnancy


Some teratogens are dangerous throughout a pregnancy and some are dangerous only at specific points of embryonic development. The only safe course of action is to actively avoid known teratogens before and during pregnancy. The list below is not all inclusive but does list some well known and dangerous agents that are proven teratogens.


Additionally, teratogens may also affect pregnancies and cause complications such as preterm labors, spontaneous abortions, or miscarriages. Teratogens are classified into four types: physical agents, metabolic conditions, infection, and finally, drugs and chemicals. The word teratogen originates from the Greek word for monster, teratos.