Does air pollution cause newborn babies to be underweight?

Mothers who breathe the kind of pollution emitted by vehicles, coal power plants and factories are significantly likelier to give birth to underweight children than mothers living in less polluted areas.

That’s according to an international study, published Wednesday, which is believed to be the largest to examine how newborns’ bodies are affected by air quality. It’s an issue that has raised particular concern in China and other developing nations.

Nearly 30 researchers, including three from the Bay Area, based their conclusions on more than 3 million births at 14 sites in North America, South America, Europe, Asia and Australia.

Focusing on children born on-time in the mid-1990s to mid-2000s, they found that, worldwide, the greater the air pollution, the less babies tend to weigh at birth.

Weighing less than 5.5 pounds at birth is a factor for chronic health issues in childhood, including a higher risk for infection and developmental delays, experts say. Problems in adulthood can include cardiovascular disease, diabetes and other metabolic disorders.

“Being low-birth weight basically is like you’re starting at a little bit of disadvantage in terms of health throughout your lifetime,” said Tracey Woodruff, the study’s co-principal investigator and director of the University of California at San Francisco’s Program on Reproductive Health and the Environment.

For the study, which appears in the journal Environmental Health Perspectives, researchers looked at two types of air pollutants, including inhalable coarse particles, which are about 10 micrometers in diameter and often appear in natural elements such as dirt, dust and sea salt.

The particles were found in various levels throughout the 14 sites. Seoul, South Korea’s air had the highest concentration, 66.5 micrograms per cubic meter, while Vancouver, British Columbia’s had the lowest, 12.5 micrograms per cubic meter.

In the United States, California’s levels – about 29 micrograms per cubic meter – exceeded those of Connecticut, Massachusetts, New Jersey and Atlanta. But the Golden State fared better than urban regions in Brazil, Italy and the Netherlands, where concentrations were in the 40s.