An infant wearing a mask was carried along a street in severe pollution in Beijing on January 12, 2013.
Hong Kong CNN  — 

Babies carried by pregnant women during the Beijing Summer Olympics in 2008, when China took drastic steps to combat air pollution, were born heavier than than babies born a year earlier or later, a new study has found.

The paper, published in the Environmental Health Perspectives journal, this week said babies that spent their eighth month in the womb during the Beijing Olympics (August 8, 2008 until September 24, 2008) were, on average, 23 grams larger at birth, compared to the same period in 2007 and 2009.

The reason? Cleaner air.

As a condition of hosting the Olympics, Beijing, one of the world’s most polluted cities, closed factories and power plants, seeded clouds and restricted traffic in order to to reduce pollution levels.

The study said that air pollutants were cut by between 18% and 59% during the Olympic period.

“Air pollution can result in lower birth weight,” said Zhang Jinliang, researcher with Chinese Research Academy of Environmental Health Sciences and an author of the report.

She added that the low birth weight didn’t necessarily mean a baby was less healthy but was more at risk during their first month and a low birth weight was related to some diseases later in life.

The study, which sampled information from 83,672 births in the Chinese capital, only found a significant link between a decrease in pollution and an increase in birth weight in the eighth month of pregnancy – when babies enjoy a growth spurt.

There was no significant link for the first to seventh months of pregnancy.

Some of the world’s most polluted cities are in China.

A landmark study released in 2013 found that air pollution cuts life expectancy in China by five and a half years.

Multinational companies find it harder to recruit executives and offer pollution bonuses and expensive air purifiers to convince them to stay.

And locals are increasingly vocal about the smog. A two-hour documentary called “Under the Dome” released online earlier this year went viral, clocking up millions of views.