A latest study has found that women in Beijing, who were in the final stage of pregnancy during the 2008 Olympics, when officials strictly controlled air pollution, gave birth to heavier babies than in years when the city was smoggier.

In the study it was found that the mothers in their eighth month of pregnancy during the Games had children which were born on average 23 grams heavier as compared to those born either a year earlier or a year later.

The study, led by epidemiologist David Rich of the University of Rochester Medical Center, hasn't found any significant association for mothers in their first through seventh months.

For the game, Beijing halted construction, shut factories and cut the numbers of vehicles allowed on the roads for 47 days to provide the basis for a natural experiment on the effects of pollution. As a result of it, people were able to capture memorable images of blue skies during the competition.

Previously, studies have associated pollution with birth weight, but they didn't pinpoint at what stage of pregnancy the association was greatest.

Researchers in China and the US used the records of over 83,000 full-term births to mothers in Beijing from 2007 to 2009.

In a statement, the study authors said, "Late pregnancy is a particularly important period of foetal growth, as during this time the foetus experiences the greatest amount of physical growth, and the development of the central nervous, cardiovascular, and musculoskeletal systems accelerates".

The study suggested that pollution may be interfering with this period of development. The authors said that pollution controls, even for short periods of time can have positive health benefits.