The greater the air pollution, the smaller the baby, study finds

Pregnant women increase the risk of having a low-birth-weight baby when they breathe in air pollution from vehicles, heating and coal power plants, an international study has concluded.

The research, the most extensive of its kind on the link between air pollution and fetal development, found that the higher the pollution, the greater the rate of children born with a low weight. It was published in the US journal Environmental Health Perspectives.

The study also found that for every 10-microgram increase in the average exposure of a pregnant woman to PM10 particles, their babies were 8.9 grams lighter at birth, adjusted for such variables as socio-economic status. PM10 refers to the amount of particles 10 microns or less in diameter in a cubic metre of air.

Scientists analysed data from more than three million births in nine nations in North America, South America, Europe, Asia and Australia. Most of the data was collected from the mid-1990s to the late 2000s, with some obtained earlier.

Low birth weight - below 2.5 kilograms - is linked to serious problems, including a higher risk of complications or death in the weeks right after birth, as well as chronic health problems later in life, says lead author Payam Dadvand, of the Centre for Research in Environmental Epidemiology in Barcelona.

Co-lead investigator Tracey Woodruff said the pollution was ubiquitous.