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.