Washington, Feb 6 : Mothers exposed to vehicular emission, urban heating and coal power plants are much more likely to bear children of low birth weight, says an international study.

The study, the largest of its kind, analysed data collected from more than three million births in nine nations at 14 sites in North America, South America, Europe, Asia and Australia.

The researchers found that higher the pollution rate, the greater the rate of low birth weight all over the world, the journal Environmental Health Perspectives reports.

It was led by co-principal investigator Tracey J. Woodruff, professor of obstetrics and gynaecology and reproductive sciences at University of California San Francisco, with Jennifer Parker, from the Centres for Disease Control and Prevention.

Low birth weight (below 2.5 kg) is tied to serious health consequences, including increased risk of post-natal morbidity and mortality and chronic health problems in later life, noted Payam Dadvand, from the Centre for Research in Environmental Epidemiology (CREAL) in Barcelona, Spain, according to a university statement.

The team assessed data collected from research centres in the International Collaboration on Air Pollution and Pregnancy Outcomes.

Most of the data assessed was collected during the mid-1990s to the late 2000s, and in some cases, earlier.

"What's significant is that these are air pollution levels to which practically everyone in the world is commonly exposed," said Woodruff.

"These microscopic particles, which are smaller than the width of a human hair, are in the air that we all breathe."

"This study comes at the right time to bring the issue to the attention of policy makers. From the perspective of world health, levels like this are obviously completely unsustainable," said study co-author Mark Nieuwenhuijsen, from CREAL.(IANS)