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Birth Defects

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California Environmental Health Tracking Program

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Last Edited: 10/5/2010

What are Birth Defects?

Birth defects are estimated to affect more than 120,000 children in the United States every year.  Birth defects are one of the leading causes of infant deaths.  An infant may be born with more than one birth defect.  Some birth defects, such as Down syndrome, can affect multiple organs.  Some infants born with birth defects have an increased likelihood of premature birth, illness, and long term disability.

What causes birth defects?

Researchers do not know the causes of all birth defects.  Many birth defects are believed to have multiple causes, including both genetic and environmental factors. Generally speaking, scientists estimate that 60% of birth defects have causes that are unknown.  More research is needed to understand the links between the environment and birth defects.

Learn about environmental factors that are potentially related to individual birth defects.


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What are the different types of birth defects?

Given the complexity of the human organism, the number of possible birth defects is vast.  On this website, we have information for 12 different birth defects.  These birth defects were selected due to their possible relationship to environmental factors or because they represent a substantial public health burden, regardless of cause.

  • Anencephaly
  • Cleft lip with or without cleft palate
  • Cleft palate without cleft lip
  • Down syndrome (Trisomy 21)
  • Gastrochisis
  • Hypoplastic left heart syndrome
  • Hypospadias
  • Lower limb deficiencies
  • Spina bifida
  • Tetrology of Fallot
  • Transposition of the great arteries
  • Upper limb deficiencies

Learn more about these birth defects.


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What are risk factors for birth defects?

There are a number of risk factors that may increase the chances of having an infant with a birth defect.  Avoiding these exposures and behaviors while pregnant can help to increase one’s chances of having a healthy infant.  For some of the risk factors listed below, scientists have raised concern about their possible roles in birth defects.  For others,  the nature of the risk has been more thoroughly established. 

Risk factors include:

  • Smoking while pregnant
  • Drinking alcohol while pregnant
  • Using recreational or certain prescription drugs while pregnant
  • Exposure to solvents
  • Exposure to pesticides
  • Chronic health conditions
  • Poor maternal nutrition
  • Lack of folic acid
  • Maternal stress

Learn more about environmental factors that are potentially related to individual birth defects.


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How are birth defects diagnosed?

Diagnosis of individual birth defects differs with the type of abnormality.  Some birth defects can be diagnosed before birth and might allow health care providers to reduce risks to the developing fetus and/or the mother herself.

A prenatal blood test during the first or second trimester of pregnancy is used to screen for certain birth defects, including neural tube defects (anencephaly and spina bifida) and chromosomal defects (Down syndrome).  These blood tests may indicate an increased risk of having a fetus with a certain birth defect.  However, they cannot definitively diagnose specific birth defects.  In California, a pregnant woman may be referred for additional testing at a specialized center.   The California Prenatal Screening Program has more information on prenatal screening for certain birth defects.

If additional testing is needed after screening, a medical provider should recommend detailed ultrasound.  He or she may also refer a woman for genetic counseling and tests such as amniocentesis or chronic villus sampling (CVS).  Some birth defects, such as heart abnormalities, may be detected during a prenatal ultrasound.  Other structural defects may only be detectable after birth.

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