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Birth Defects

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California Environmental Health Tracking Program

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Last Edited: 10/7/2010

Birth Defects and the Environment

The causes of the majority of birth defects are unknown.  It is often challenging to find a link between specific environmental exposures and birth defects.  It is thought that many birth defects may be caused by a mix of genetic, behavioral, and environmental factors.

How could birth defects be related to the environment?

Over 83,000 chemicals are used in homes and workplaces in the United States, but there is little information on their effects during pregnancy.  Research continues to help us better understand the relationship between birth defects and the environment.

A pregnant woman may be exposed to chemicals through breathing, eating, and absorption through the skin.  The developing fetus can then be exposed to chemicals found in the mother’s blood.  Chemicals can pass through the placenta and into the fetus’s bloodstream. 

The baby's development may be more susceptible to environmental exposures during the first trimester.  This is the most sensitive time in pregnancy, when the organs and limbs are formed.


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Examples of environmental concerns

Air Pollution and Heart Defects

Air pollutants are particles, liquids, and gases which have harmful chemical properties. These pollutants are often found in large concentrations in urban areas but may affect rural communities as well.  Air pollutants have been shown to be a risk factor for some birth defects such as heart abnormalities.1  Common air pollutants include:

The risk of birth defects, particularly heart abnormalities, may increase when women are exposed to higher amounts of ozone and carbon monoxide in the second month of pregnancy. 

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Pesticides and Gastroschisis

Pesticides are chemicals used to control insects, weeds, fungus, and other pests.  They are often used in homes, agricultural areas, and workplaces.  According to the March of Dimes, all pregnant women should avoid exposure to pesticides whenever possible.  Pesticides are commonly used in:

  • Agriculture
  • People’s homes
  • Landscaping
  • Commercial buildings

Research suggests that maternal exposure to atrazine, a herbicide used to eliminate weeds in agricultural areas, could be associated with gastroschisis, a birth defect of the intestines.  Prenatal exposure to higher concentrations of surface water atrazine, particularly with spring conceptions, may affect the increased prevalence of gastroschisis.2

The Environmental Health Investigations Branch has more information about pesticides.  Visit CEHTP's Agricultural Pesticide Mapping Tool to see if agricultural pesticides are used near your community.

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Other environmental concerns

According to the CDC and the March of Dimes, there is broad concern about the following environmental factors and their suspected relationship to some birth defects.

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Arsenic is a toxic element that occurs naturally in the environment and as a byproduct of some industrial activities.  It poses a risk when pregnant  women are exposed to it in high levels.  Individuals are at greater risk for of arsenic exposure if they:

  • Work or live near metal smelters
  • Live in agricultural areas where arsenic fertilizers were used on crops
  • Live near hazardous waste sites or incinerators
  • Drink well water with high levels of arsenic

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Disinfection Byproducts

Disinfection byproducts come from chemicals used in our drinking water to kill microorganisms such as bacteria and viruses.  Exposure to disinfection byproducts in drinking water, such as trihalomethanes (THM), may increase the risk of birth defects that affect development of the brain, spinal cord, urinary tract, and heart.

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Exposure to mercury while pregnant may harm the infant’s nervous system development.  There are two forms of mercury: elemental (pure) mercury and methylmercury.  Elemental mercury is found in:

  • Some thermometers
  • Dental amalgam fillings
  • Fluorescent light bulbs
  • Some batteries

Methylmercury is formed when mercury in the air is deposited in water.  People are usually exposed to this form of mercury when they consume fish.  Large fish tend to contain large amounts of mercury.  Examples include:

  • Swordfish
  • King mackerel
  • Tilefish
  • Shark

Pregnant women are advised to restrict their consumption of fish, and avoid these species in particular.  The Environmental Health Investigations Branch has more information about mercury in fish.  


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Two chemicals found is plastics- Bisphenol A and phthalates- have raised concerns over their potential link to birth defects.  Bisphenol A (BPA) is used to manufacture polycarbonate plastic and epoxy resins.  BPA may affect brain, behavior, and prostate gland development in fetuses, infants, and children.  BPA is found in the epoxy resins used to line:

  • Metal food cans
  • Metal lids of glass jars
  • Some reusable clear plastic water bottles
  • Some clear plastic baby bottles

Phthalates are added to make plastics more flexible and durable.  They can be found in:

  • Building materials
  • Adhesives
  • Children’s toys
  • Paints
  • Food products
  • Personal care products
  • Household items
  • Other products

Phthalates are found in higher concentrations in children than in adults.  Research indicates that phthalates may increase the risk of birth defects such as hypospadias

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Solvents are chemicals that dissolve other substances.  Exposure to solvents during pregnancy, particularly during the first trimester, may increase risk of neural tube and heart defects.  Common solvents include:

  • Gasoline
  • Motor oil
  • Paint thinner
  • Polyurethane
  • Spray paint
  • Aerosol sprays
  • Nail polish remover
  • Some cleaning products (such as oven cleaners)

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1.  Ritze, B, et al. Ambient Air Pollution and Risk of Birth Defects in Southern California. American Journal of Epidemiology. 2002; 155:1,17-25.  

2.  Waller, SA, Paul, K, Peterson SE,et al. Agricultural-related Chemical Exposures, Season of Conception, and Risk of Gastroschisis in Washington State. Am J Obstet Gynecol 2010;202:241.e1-6.