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11-10-2011 | Gynaecology | Article

Exposure to air pollution may increase preterm birth risk in pregnant women

Abstract

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MedWire News: Exposure to environmental air pollution from road traffic significantly increases the risk for preterm birth in pregnant women in a dose-dependent manner, say researchers.

Michelle Wilhelm (University of California, Los Angeles, USA) and colleagues assessed the exposure to air pollutants of 241,415 Californian women who gave birth in the state between June 2004 and March 2006. Women who gave birth to twins, had babies with recorded birth defects, or who had missing gestational age or weight data were excluded.

The women all lived within five miles of a Southern California Air Quality Management District Multiple Air Toxics Exposure Study monitoring station.

Using data obtained from the station, the researchers calculated the women's exposure to polycyclic aromatic hydrocarbons (PAHs), particulate matter with a diameter of less than 2.5 μm (PM2.5), criteria air pollutants (from government monitoring data), and land use regression estimates of nitric oxide (NO), nitric dioxide (NO2), and nitrogen oxides (NOx).

Wilhelm and colleagues found that for each inter-quartile range increase in whole pregnancy exposure to organic and elemental carbon, benzene and diesel, burning biomass, and ammonium nitrate PM2.5, the risk for preterm birth increased by 6-21%.

Similarly, each inter-quartile range increase in PAH exposure in pregnancy increased the risk for preterm birth by 30%.

There was a small association between NO, NO2, and NOx exposure and preterm birth, but only in the range of a 3-4% increase in risk per inter-quartile range increase in exposure.

"Air pollution is known to be associated with low birth weight and premature birth. Our results show that traffic-related PAH are of special concern as pollutants, and that PAH sources besides traffic contributed to premature birth," said study co-author Beate Ritz, also from the University of California, Los Angeles.

"The increase in premature birth risk due to ammonium nitrate particles suggests secondary pollutants are also negatively impacting the health of unborn babies. To reduce the effects of these pollutants on public health, it is important that accurate modeling of local and regional spatial and temporal air pollution be incorporated into pollution policies," she added.

Writing in the journal Environmental Health, the researchers conclude: "Future studies should focus on accurate modeling of both local and regional spatial and temporal air pollution distributions, and incorporate source information to help better inform policy decisions on air pollution control."

By Helen Albert

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