Exposure to air pollutants for pregnant women with asthma at both early and later gestational weeks carried a higher risk for preterm birth, according to new data.

“Women with asthma have higher risks for preterm birth after acute exposure to most criteria air pollutants both early (weeks 23, 26, and 29) and later in gestation (weeks 34-36),” Pauline Mendola, PhD, of the division of intramural population health research at Eunice Kennedy Shriver National Institute of Child Health and Human Development in Rockville, Maryland, and colleagues wrote.

Preconception and the first weeks of pregnancy appear to be important windows of susceptibility for preterm birth risk with respect to carbon monoxide, nitrogen oxide, PM10 and PM2.5 exposure, they said.

Mendola and colleagues evaluated 223,502 US deliveries with a modified version of the Community Multiscale Air Quality model for preterm birth risk from maternal asthma and exposure to pollutants in the air, according to the abstract. The researchers analyzed CO, ozone (O3), sulfur dioxide (SO2), NO, PM2.5 and PM10 exposure for each gestational week, with preterm week 23 to week 36 delivery results compared with women who remained pregnant.

Although there were no significant trends regarding preterm birth prior to gestational week 30, the researchers found preterm birth was more common between weeks 34 and 36, according to the abstract. Specifically, Mendola and colleagues found maternal asthma plus exposure to NOx, CO and SO2 between weeks 34 and 36 carried an elevated risk of pre-term birth, with an inverse association between ozone and preterm birth at week 34.

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