What are Teratogens by Trinh Nguyen

Teratogens are substances (viruses, chemicals, and drugs) and conditions (environmental stress, and severe malnutrition) that are harmful during prenatal development.  If pregnant women are exposed to these substances they’re at an increase risk of prenatal abnormalities and perhaps death of the baby. The substances not only cause physical harm but also impaired learning and behavior. There are several influential factors of teratogens: timing of exposure, amount of exposure, and genetic vulnerability.

An example of a teratogen is the varicella, which is also known as the “chicken pox”.  It is a highly infectious disease usually associated with childhood. By adulthood, ninety-five percent of adults in America have had chicken pox. Eighty-five to ninety-five percent of pregnant women are immune to the disease. Though, chances of pregnant women getting chicken pox are rare, 7 out of 10,000 women will catch the virus because they’re not immune to the virus. Infection of the fetus occurs 1 to 5 per 10,000 pregnancies and induces the risk of birth defects known as varicella embryopathy or congenital vericella syndrome. The birth defects include scars, defects of muscle and bone, paralyzed and malformed limbs, blindness, seizers, a small head size, and mental retardation.

Chicken pox is caused by the virus varicella-zoster virus (VZV)—a form of herpes virus.  Transmission occurs by airborne or person-to-person direct contact. Once a person is exposed to the virus, it may take up to 14 to 18 days to develop. Risks vary depending on the timing of the exposure, but the syndrome is rarely seen if the infection occurs 20 weeks of pregnancy, thus the crucial period (the greatest susceptibility) is the first 20 weeks of pregnancy. Another critical period is during the newborn stage (after conception) — the mother develops the rash five days before, to two days after delivery. In this case, between 25 to 50 percent of newborns will be infected and if not treated, 30 percent of newborn babies will die. There’s only a mild infection if the mother develops the rash between six to 21 days before delivery because the maternal antibodies partly protect the fetus.

For the varicella teratogen, timing and the amount of exposure determines the risks of the prenatal abnormalities, not so much as for the genetic vulnerability. Education and preventative measures are the best strategies to avoid the congenital vericella syndeome. If the soon to be mothers are well educated about chicken pox and are informed on the ways to prevent from being infected, few chances are that their newborns will be at risk of birth defects. In 1995, the Food and Drug Administration administered a chicken pox vaccine, varicella-zoster immune globulin (VZIG), to be immediately administered to the newborn after birth to prevent the infection. Also, if a pregnant woman has been exposed to an infected person, VZIG can be given within 96 hours to prevent the infection.  Another preventative measure is for pregnant women to completely avoid exposure to anyone infected even if they’re not sure of their immunity.

 

References

http://www.chp.edu/CHP/P02161

http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=GB&Expert=291