Exposure to two common airpollutants may increase the chance that a pregnant woman will give birth to achild with certain heart defects, according to a UCLA study that provides thefirst compelling evidence that air pollution may play a role in causing somebirth defects.
Pregnant Los Angeles-area women living in regions with higherlevels of ozone and carbon monoxide pollution were as much as three times aslikely to give birth to children who suffered from serious heart defects,according to a study published in the Jan. 1 edition of the American Journal ofEpidemiology.
Researchers from the UCLA School of Public Health and theCalifornia Birth Defects Monitoring Program found the risk for the birthdefects increased among women exposed to elevated amounts of the pollutants inthe second month of their pregnancy, a period when the heart and other organsbegin developing.
"The greater a woman's exposure to one of these two pollutants inthe critical second month of pregnancy, the greater the chance that her childwould have one of these serious cardiac birth defects," said Beate Ritz, a UCLAepidemiologist who headed the study. "More research needs to be done, but theseresults present the first compelling evidence that air pollution may play arole in causing some birth defects."
Researchers conducted the study by matching extensive airpollution monitoring information collected by regional air-quality officialswith information from the California Birth Defects Monitoring Program, aprogram funded by the state Department of Health Services that collectscomprehensive information about structural birth defects in partnership withthe March of Dimes Birth Defects Foundation.
"The birth defects registry is an exquisite investigational tool.Because of this resource we are able to intensify the search for causes ofbirth defects," said John A. Harris, chief of the California Birth DefectsMonitoring Program. "One in 33 babies in the United States is born with aserious birth defect — the leading cause of infant death. This kind of researchis not a luxury. Studies like this one on air pollution give us critical leadsto follow up with further research."
Ritz said she was surprised that the study found an effect at thepollution levels researchers studied.
"Thesefindings show that there are more health problems caused by air pollution thansolely asthma and other respiratory illnesses," Ritz said. "There seems to besomething in the air that can harm developing fetuses."
The study also suggests that despite a significant decrease inurban air pollution nationally, there may be pollution problems that are notyet understood.
"There has been a big reduction in the levels of criteria airpollutants like ozone and carbon monoxide over the years," Ritz said. "Butthere still may be air toxics and fine particles or other secondary pollutantsthat occur alongside carbon monoxide and ozone, but which we don't measureroutinely or know about, and those things may pose health risks we don't yetunderstand."
Researchers analyzed information collected by the California BirthDefects Monitoring Program on more than 9,000 babies born from 1987 to 1993 inLos Angeles, Orange, San Bernardino and Riverside counties. Using measurementsmade regularly at 30 locations by the South Coast Air Quality ManagementDistrict, which manages air quality in the four-county region, researcherscompared air quality near the homes of children born with birth defects to airquality in the neighborhoods of children born healthy.
Pregnant women who were exposed to increased levels of ozone andcarbon monoxide faced an elevated risk of having a child with conotruncal heartdefects, pulmonary artery/valve defects and aortic artery/valve defects. Thisgroup of heart defects occurs 1.76 times per 1,000 births, with about 935 casesin California each year. Many of these babies face open-heart surgery beforeage one.
For women living in the areaswith the highest levels of carbon monoxide and ozone, the risk tripled whencompared to women who lived in areas of the air basin with the cleanest air.Among women who lived in areas with moderately higher pollution levels, therisk of birth defects doubled.
"We're not sure carbon monoxide is the culprit because it could bejust a marker for something else in tailpipe exhaust," said Gary Shaw of theCalifornia Birth Defects Monitoring Program and a co-author of the study. "Thefact that certain heart defects are turning up in the second month of pregnancywhen hearts are being formed suggests something serious may be happening. Thedose-response aspect of this study certainly strengthens the findings andunderscores the need for additional research. Unlike other health factors likediet or lifestyle, a pregnant woman has almost no control over the quality ofair she breathes — we need answers."
Researchers did not find a link between birth defects and exposureto nitrogen dioxide and larger-sized particulate matter — other air pollutantsthat are commonly found in the South Coast Air Basin and other urban regions.However, the monitoring network for particulate matter is less extensive thanfor other pollutants and no monitoring is done for very small particulates,which are often found alongside carbon monoxide. The study also found nocorrelation between exposure to air pollution and other common birth defectssuch as cleft palates.
While the study focused on the Los Angeles urban region,the findings have implications for most urban areas in the nation, particularlyones where vehicle traffic plays an important part in forming air pollution,Ritz said. Carbon monoxide is primarily released in tailpipe emissions, whileozone pollution is formed in the atmosphere from pollutants released by bothvehicles and industrial sources.
A number of recent studies conducted by Ritz and other researchershave suggested that air pollution can have harmful effects on pregnancy,including causing premature delivery and low birth-weight. But researchers hadnot been able to examine whether there is a link between air pollution andbirth defects because they lacked the resources to do such a study.
"You cannot do this type of scientific research unless you have asurveillance system that collects this type of high-quality information," Ritzsaid. "Unless we collect extensive air pollution monitoring information anddetails about birth defects, we cannot learn about these types of healtheffects."
While the study is the first rigorous effort to demonstrate a linkbetween air pollution and birth defects, the findings do have limitations, Ritzsaid.
Researchers were only able to estimate mothers' exposures toroutinely measured air pollutants. They relied on air pollution concentrationscollected at the air-quality monitoring station nearest a mother's home, whichcould be as far as 10 miles away. Also, they were unable to evaluate otherpotential risk factors for birth defects, including maternal smoking,occupational exposures, vitamin supplement use, diet and obesity.
Future studies need to address these limitations, as well asexamine whether it is the routinely measured pollutants or other potentiallyharmful substances in air pollution that are responsible for the birth defects,Ritz said.
"There may be some other chemical culprit in tailpipe emissions,which we can't identify at this time, that is causing the problem," Ritz said."Since carbon monoxide is released in motor vehicle exhaust along with theseother pollutants that we don't measure, these other pollutants also may beimportant."
Researchers at the Southern California Particle Center are workingto identify the chemical components of the microscopic soot that is containedin vehicle tailpipe emissions. The UCLA School of Public Health-based center,one of four major particulate centers funded by federal officials, hasidentified compounds that researchers suspect could affect human health.
Funding for the study was provided by the National Institute ofEnvironmental Health Sciences. Other authors include Fei Yu of the UCLA Schoolof Public Health and Scott Fruin of the UCLA School of Public Health and theCalifornia Air Resources Board.