Air Pollution Raises Risk of Low Birth Weight Babies

The largest study ever conducted on air pollution's impact on newborn health has found that pregnant women exposed to black soot from urban vehicles and coal-fired power plants are more likely to have low birth-weight babies.  

The study by an international group of researchers analyzed data on three million births collected at 14 sites in nine countries in North America, South America, Asia and Australia.  It covered about 15 years beginning in the mid-1990s.

The massive survey found that at all these sites, pregnant women who breathed the most polluted air - as measured by carbon soot concentrations - were significantly more likely to have babies with low birth weights - below 2,500 grams or 5.5 pounds.  At that size, a baby - if he or she survives infancy - is at risk of chronic health problems and learning disabilities later in life.

Particulate air pollution is determined by a combination of soot particles' concentration in a cubic meter of air, and their size, measured in microns.  Tracey Woodruff, a professor of obstetrics and gynecology at the University of California San Francisco, and a co-principal investigator on the study, says this microscopic dust - smaller than the width of human hair - is in the air we all breathe.  Its impact on our health varies with the concentration and size of the particulate matter.  Woodruff says a relatively low concentration of 10-micron soot particles. . .

“...was associated with a 3 percent increase in the risk of having a low birth-weight baby," said Woodruff. "So the risk at the individual level is modest, but we’re talking about many, many, many women around the world (being) exposed.”

In the United States, Clean Air laws require that soot particles measure less than 2.5 microns in size, at concentrations of no more than 12 micrograms per cubic meter.  In Europe, the limit is 25 micrograms.  In Beijing, China, soot concentrations were measured recently at more than 700 micrograms per cubic meter.  Urban areas in South Asia are also reporting dangerously high soot concentrations.

Woodruff says there are several possible reasons why this kind of air pollution causes low birth-weight in infants.

“It could be that because particulate air pollution is affecting the health of the mother, that that in turn affects the health of the developing fetus," she said. "Or it could be that some of these particles actually have the ability to go into your lungs and then some of the toxic materials on the particle can get into your blood stream, and maybe that can go down to the fetus and affect development in that way.”

The scientists got their data from centers participating in the International Collaboration on Air Pollution and Pregnancy Outcomes, a global research initiative launched in 2007 to assess the impact of urban air pollution on pregnancy and newborn health.