Pregnant women with asthma may be at an increased risk for preterm births if they are exposed to high levels of air pollution from vehicles, according to new research. The study, published March 1 in the Journal of Allergy and Clinical Immunology, found that short-term and extended exposure to nitrogen oxides and carbon monoxide was associated with preterm deliveries, particularly when asthmatic women were exposed to those pollutants just before conception and in early pregnancy.
“Preterm birth is a major public health problem in this country – affecting more than 1 in 10 infants born in the United States,” Pauline Mendola, PhD, lead study author and an investigator at the National Institutes of Health’s (NIH) Eunice Shriver National Institute of Child Health and Human Development, said in an NIH news release. “Our study found that air pollution appears to add to the preterm birth risk faced by women with asthma,” Mendola added.
Asthma affects an estimated 9 percent of women of reproductive age in the U.S. While other studies have looked at the effects of air pollutants on preterm births, the research conducted by Mendola and her colleagues is the first to examine the ramifications of exposure before conception.
For the study, the researchers analyzed data from a sample of 223,502 singleton pregnancies delivered in 19 hospitals around the country from 2002 to 2008. Included in the information was the women’s asthma status and date of delivery.
The research team matched collected data with daily measures of air quality from the regions surrounding each of the hospitals to assess the potential impact of air pollution on preterm delivery. The researchers took into account such factors as location, age, race and ethnicity, pre-pregnancy weight, smoking and alcohol use, and chronic maternal health issues.
Findings showed that increased exposure to nitrogen oxide in the three months before pregnancy increased the risk of giving birth prematurely by 30 percent for women with asthma, compared to 8 percent for women who did not have the disease. Higher exposure to carbon monoxide during the same period raised the risk of preterm birth by 12 percent for women with asthma, but had no effect on women who were not asthmatic.
The research team also found that exposure to high levels of particulate matter air pollution – very small particles of substances such as acids, metals and dust in the air – in the last six weeks of pregnancy were linked to a higher risk of premature birth.
Mendola suggested one explanation for the link between air pollution and premature birth is that exposure to environmental pollutants may cause inflammation or other internal stresses that interfere with embryo implantation or placental development. Acknowledging that more research is needed, she advised women with asthma who are pregnant or trying to conceive to avoid exposure to air pollution whenever possible.
“There are already guidelines calling for people with asthma to avoid ambient exposure on bad air pollution days,” she told MedPage Today. “This may be especially important for women with asthma who are pregnant or trying to become pregnant.”