Exposures Causing Birth Defects

Studies suggest that up to 80 percent of pregnant women are exposed to at least one medication or chemical during the course of a pregnancy. It is known that some of these exposures can harm a developing fetus. Environmental factors that can cause birth defects or have a harmful effect on the developing fetus during pregnancy are called teratogens.

Maternal exposures may cross the placenta and directly affect the fetus. Paternal exposures may affect the sperm, which could possibly cause a genetic mutation or alter fertility. However, at present, there is no data to suggest teratogenic effects from any paternal exposures.

It is important to keep in mind that 1 to 5 percent of all infants are born with one or more birth defects. Some are recognizable genetic disorders (such as Down syndrome and muscular dystrophy), some are caused by known teratogens (eg: alcohol, rubella), and many have no identifiable cause. A great deal of research continues to try to determine the cause of various birth defects. Types of teratogens currently known include:

  • Medications/drugs – eg: Accutane, alcohol
  • Infections – eg: rubella (German measles)
  • Maternal disease – eg: diabetes
  • Heat – eg: persistent high fever
  • Heavy metals – eg: lead, mercury

Both timing of and the dose or amount of exposure are critical when attempting to determine risk for teratogenic effects. For example, if a child is born with a heart defect and the mother reports she had two glasses of wine when she was eight months pregnant, she can be reassured that the baby’s heart defect was not caused by the wine she drank because the heart’s structure developed during the first few weeks of pregnancy. Whatever caused the heart defect would have occurred at conception, if genetic, or during the time the heart was being formed if caused by a teratogen.

Teratogens have a spectrum of potential effects depending on the agent, the dose/amount and the timing of exposure.

Potential effects include:

  • Miscarriage
  • Growth retardation
  • Major and/or minor malformations
  • Metabolic dysfunction ( hypoglycemia, hypothyroidism)
  • Neurobehavorial dysfunction (irritability, lethargy, attention deficit, mental retardation)

Several Teratogen Information Services have been established in the U.S. and in other countries to provide information and risk assessment for pregnant women and health care providers and  to gather prospective information about fetal risks. The first Teratogen Information Service was established over 25 years ago in San Diego and continues to provide confidential pregnancy risk information as a free service to pregnant women and their health care providers.

For more information on tetrogens and pregancy risk, call the California Teratogen Information Service at 800-532-3749 or visit www.ctispregnancy.org.

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