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aortic artery/valve defect
chromosome abnormalities
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oral cleft
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ventricular septal defect

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air pollution

Combining our registry data with detailed air quality surveillance records, researchers are able to address for the first time whether air pollution causes birth defects.

UCLA scientists mapped addresses for children with and without birth defects to one of 30 air monitoring stations operated by the South Coast Air Quality Management District. Calculating from dates of birth, average levels of 4 pollutants were estimated for the first, second and third months of each gestation.


Higher levels of 2 pollutants during the second month of pregnancy increased risk for specific heart defects:

bullet Carbon monoxide was linked to ventricular septal defects.
bullet Ozone was linked to conotruncal heart defects, pulmonary artery/valve defects and aortic artery/valve defects.

There was a dose-response association: increasing exposure was linked to greater risk for heart defects. Those in the highest exposure brackets had about twice the risk of those with least exposure.

We found no clear effect for oral clefts, other heart defects or chromosome abnormalities.


An association between air pollution and birth defects is biologically plausiblemajor heart development occurs during the second month of gestation. Hypoxia (decreased oxygen) is associated with heart and other defects in animal studies. And smokingwhich creates carbon monoxide and hypoxiaincreases risk for oral clefts.

We can't be sure if the pollutants studied here are the culprits, however. Carbon monoxide levels reflect automobile exhaust and may be a marker for some other component of tailpipe emissions.

The study's exposure information was relatively incompletefor example, it didn't consider other exposure sources such as mothers' smoking or commuting patterns. And, residence at birth may be different than in early pregnancy. That an effect was seen despite these limitations is intriguing and warrants further research.

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about air pollution

picture of smog

Our study looked at 4 air pollutants:

bullet Carbon monoxide is found in car exhaust and industrial emissions, as well as in cigarette smoke. It interferes with the blood's ability to absorb and transport oxygen. Pregnant women breathing high levels of carbon monoxide are more likely to have low birthweight infants.
bullet Ozone is a byproduct created when other pollutants react in sunny conditions. It can irritate the lungs and airways.
bullet Nitrogen dioxide forms when automobile and industrial emissions combine with oxygen. It irritates the lungs and may suppress the immune system or promote DNA changes.
bullet Particulate matter is created by combustion from automobiles and industry as well as mechanical processes, such as tire wear. It can cause lung damage.

For more information on the health effects of air pollution:
bullet South Coast Air Quality Management District
bullet AQMD Student's Health Page
bullet Environmental Protection Agency



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