Pregnant women with asthma may be at greater risk of preterm birth when exposed to high levels of certain traffic-related air pollutants, according to a study by researchers at the National Institutes of Health and other institutions.
The researchers observed an increased risk associated with both ongoing and short-term exposure to nitrogen oxides and carbon monoxide, particularly when women were exposed to those pollutants just before conception and in early pregnancy.
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For example, an increase of 30 parts per billion in nitrogen oxide exposure in the three months prior to pregnancy increased preterm birth risk by nearly 30 percent for women with asthma, compared to 8 percent for women without asthma. Greater carbon monoxide exposure during the same period raised preterm birth risk by 12 percent for asthmatic women, but had no effect on preterm birth risk for non-asthmatics.
The last six weeks of pregnancy was another critical window for women with asthma, according to the researchers. Exposure to high levels of particulate matter — very small particles of substances like acids, metals, and dust in the air — also was associated with higher preterm birth risk.
The study was published online in the Journal of Allergy and Clinical Immunology.
“Preterm birth is a major public health problem in this country, affecting more than 1 in 10 infants born in the United States,” said Pauline Mendola, Ph.D., lead author and an investigator at the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. “Our study found that air pollution appears to add to the preterm birth risk faced by women with asthma. These findings set the stage for further studies designed to help prevent preterm birth in this at-risk group.”