Automobile Pollution May Increase Preterm Birth Risk for Pregnant Women with Asthma: Study

Pregnant women with asthma may face an increased risk of experiencing pre-term labor if they were exposed to automobile air pollution early in the pregnancy, or just before conceiving, according to the findings of new research. 

In a study published this week in the Journal of Allergy and Clinical Immunology, researchers found that asthmatic women who had exposure to the pollutant nitrogen oxide within the three months before pregnancy have a 30% increased risk of having their child early when they become pregnant. This is compared to an eight percent increased risk for women who do not have asthma under the same conditions.

Researchers also found women with asthma who had greater exposure to carbon monoxide during the same period had an increased preterm birth risk by 12%; whereas women without asthma had no effect or increased preterm birth risk.

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Preterm labor includes any birth before 37 weeks of pregnancy, which carries a high risk for complications.

The study was conducted by researchers at the National Institute of Health Eunice Kennedy Shriver National Institute of Child Health and Human Development, the University of North Texas Health Science Center in Fort Worth, National Institute for Health and Welfare in Oulu, Finland, the Emmes Corporation in Rockville, Maryland, and Texas A&M University in College Station.

Researchers compiled data from a national sample of 223,000 women who were pregnant with one child, delivered at 19 hospitals around the country from 2002 to 2008. Electronic medical records of the women included their asthma status and date of delivery.

That data was then matched 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. Researchers studied six pollutants and accounted for factors like location, age, race and ethnicity, pre-pregnancy weight, smoking and alcohol use and chronic maternal health conditions.

Overall air pollution from certain traffic-related air-pollutants was linked to a higher risk of preterm birth for mothers with asthma. Exposure to high levels of particulate matter was also associated with higher preterm birth risk. Particulate matter is very small particles of substances like acids, metals and dust in the air.

“In this case, it may be that early exposure to air pollution sets off inflammation or other internal stresses that interfere with embryo implantation or placental development,” said Pauline Mendola, Ph.D., lead author and an investigator at the National Institute of Health. “Those disruptions could lead to preterm delivery down the road. More research will help us to better understand the potential impact of air pollution in the months surrounding conception.”

The increased risk was associated with ongoing and short-term exposure to nitrogen oxides and carbon monoxide, especially when the mothers were exposed to the traffic 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,” said Mendola.

Another recent study found that women exposed to high levels of pollution during pregnancy have a higher risk of having children who have lower IQ scores later in childhood. The pollution also affected the children’s perceptual reasoning and working memory, compare to children of women who were not exposed to the pollutants.

A 2013 study found a link between environmental pollution exposure during pregnancy and a twofold increased risk of the child developing autism.

Asthma affects nine percent of women of reproductive age in the U. S., according to data from the U.S. Centers for Disease Control and Prevention. Maternal asthma has been linked to a higher risk of pregnancy complications and health problems for the infants.

This study first to examine whether exposure to air pollution before conception might affect later pregnancy.


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