Air pollution increases preterm birth risk for women with asthma

Published Online: March 1, 2016

Preterm birth is a major public health problem, affecting more than 1 in 10 infants born in the United States.  Asthma is common among US pregnant women and women with asthma have a higher risk of preterm birth.  Until recently, however, research has not assessed the potential impact of air pollution on preterm birth risk among asthmatic women.

In a recent paper in The Journal of Allergy & Clinical Immunology (JACI), Mendola and colleagues analyzed data from a national sample of 223,502 singleton pregnancies to determine 1) whether air pollution exposure increases risk for mothers with asthma to a greater extent than those without asthma, and 2) if there are times during pregnancy when air pollution has a greater impact on preterm birth risk. Information on maternal asthma status, date of delivery and the gestational age of the infant was obtained from electronic medical records. The team matched that data with daily measures of air quality from the regions surrounding each of the hospitals to assess the potential effects of air pollution, week by week, on preterm birth risk. In addition to the weekly analyses, the researchers investigated broader time windows including chronic exposure to air pollution before conception which has not been studied before in relation to preterm birth. They studied six air pollutants and accounted for such factors as location, age, race and ethnicity, pre-pregnancy weight, smoking and alcohol use, and chronic maternal health conditions.

The researchers observed an increased preterm birth risk for women with asthma 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 during early pregnancy.  For example, an increase of 30 parts per billion (ppb) 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 was not associated with preterm birth risk for non-asthmatics.

The author’s findings suggest that women with asthma may be particularly vulnerable to air pollution exposure with higher preterm birth risk than women without asthma at the same exposure levels.  These risks are significantly higher for traffic-related pollutants such as nitrogen oxides and carbon monoxide.  Air pollution exposures preconception, in early pregnancy and during the weeks immediately prior to delivery appear to be important.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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