Most birth defects result from a combination of genetic, environmental, and behavioral factors. For many birth defects, it is unclear how these factors work together.
The incidence of birth defects is not distributed equally among the population. Several differences, or disparities, exist in the rates of some birth defects. Different population groups in the United States and in California experience different burdens of some birth defects.
Disparities in health outcomes can sometimes provide clues regarding the causes of disease. Perhaps more importantly, they enable us to understand the patterns of health outcomes as social justice issues.
To learn about risk factors for specific birth defects, see the California Birth Defects Monitoring Program's Birth Defects Fact Sheets.
Some racial and ethnic groups have proportionally higher rates of birth defects than others. Each type of birth defect, however, has a different distribution. For example:
- Existing racial and ethnic disparities in preterm birth rates may also put some infants at greater risk for birth defects such as congenital heart defects
- Rates of neural tube defects, including anencephaly and spina bifida, are significantly higher among Hispanics than among other racial and ethnic groups in the United States
- Some research also suggests that the rate of Down syndrome may vary by race/ethnicity-- after accounting for maternal age, Hispanic infants were born with Down syndrome at higher rates than other infants
- Asians have been shown to be at higher risk for oral-facial clefts, followed by Whites and African Americans
- Rates of hypospadias have been shown to be higher in Whites when compared to other racial/ethnic categories
No one fully understands why some groups have higher or lower rates of different birth defects. Possible explanations include the effects of poverty and racism, environmental exposures, diet, unequal access to healthcare, unequal treatment in the health care system, and genetic factors.
Maternal age has been shown to be a risk factor for some birth defects.
For example, the risk of having an infant with Down syndrome, in particular, increases with maternal age.
- At age 35, the risk is about 1 in 400
- At age 40, the risk is about 1 in 100
- At age 45, the risk is about 1 in 30
Some research also suggests that infants born to adolescent mothers may be at an elevated risk for gastroschisis.
Environmental factors may contribute to geographic disparities in birth defects. For example:
- Living near a hazardous waste site has been identified as a possible risk factor for birth defects such as neural tube defects
- Living near high traffic areas with elevated rates of air pollution may put some pregnant women at risk for having an infant with birth defects
- Residing near a water source treated with disinfection byproducts such as trihalomethanes may increase the risk of some types of birth defects, including neural tube, heart, and urinary tract defects
Learn more about environmental factors that are potentially related to individual birth defects.