Teratogens
What is a teratogen?
A teratogen is an agent, which can cause a birth defect. It is usually
something in the environment that the mother may be exposed to during her
pregnancy. It could be a prescribed medication, a street drug, alcohol
use, or a disease present in the mother which could increase the chance
for the baby to be born with a birth defect. About 4 to 5 percent of birth
defects are caused by exposure to a teratogen.
What are the most sensitive periods for teratogens in
pregnancy?
Once the egg is fertilized (conception), it takes about six to nine days
for implantation (anchoring into the uterus) to occur. Once the fertilized
egg is connected to the uterus, a common blood supply exists between the
mother and the embryo. In other words, if something is in the mother's
blood, it can now cross over to the developing fetus. Teratogens are
thought to have the ability to effect the fetus about 10 to14 days after
conception.
During the development of a baby, there are certain organs forming at
certain times. If a teratogen has the potential to interfere with the
closure of the neural tube, for example, the exposure to the teratogen
must occur in the first 3.5 to 4.5 weeks of the pregnancy, since this is
when the neural tube is closing. 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.
Alcohol, at any time during the pregnancy, has the potential to cause
birth defects and health problems in the baby, since the central nervous
system is sensitive to teratogens the entire nine months of gestation.
This is why alcohol consumption should be avoided in its entirety during
pregnancy.
There are many different teratogens that cause birth defects. Listed in
the directory below are some, for which we have provided a brief overview.
If you cannot find the information in which you are interested, please
visit the Medical Genetics Online Resources page
in this Web site for an Internet/World Wide Web address that may contain
additional information on that topic.
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