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Birth Defects

Exposure and Risk

In the United States, about 3% of babies are born with structural birth defects. Most birth defects are thought to be caused by a complex mix of genetic, behavioral, and environmental factors, although, for many birth defects, exactly how these factors work together is unclear.

An Asian grandmother hugging her granddaughter


It is not clear how many birth defects are related to environmental exposures, such as chemicals, drugs, and ionizing radiation. Some endocrine-disrupting chemicals, including polychlorinated biphenyls (PCBs), dioxins, and pesticides, have been linked to nervous system defects and developmental problems such as reduced muscle tone and response. But, we need more data to make these connections clearer.

Living near a hazardous waste site has been identified as a possible risk factor for birth defects including: spina bifida, cleft lip or palate, gastroschisis, hypospadias, chromosomal congenital anomalies such as Down syndrome, and some heart and blood vessel defects.

Exposure to disinfection by-products in drinking water such as trihalomethanes, or THM, may increase the risk of some types of birth defects which affect the brain and spinal cord, the urinary tract, and the heart.

We know the cause of some birth defects but for most we dont. We do know that some women have a higher chance of having a child with a birth defect:

  • Women who take certain drugs, smoke, or drink alcohol during pregnancy.
  • Women with certain medical conditions, such as diabetes or obesity.
  • Women who take certain medications, such as isotretinoin (a drug used to treat severe acne).
  • Women who have someone in their family with a birth defect. To learn more about your risk of having a baby with a birth defect, you can talk with a clinical geneticist or a genetic counselor.
  • Women over the age of 35 years have a higher chance of having a child with Down syndrome.
  • Teenage mothers are more likely to have a baby born with gastroschisis—a defect in the abdominal wall.
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