Researchers have found that high levels of air pollution affect fetal growth, leading to babies who are significantly underweight at the time they were born.

In a study published in the Environmental Health Perspectives, researchers showed that when air pollution levels improved, like during the Beijing Olympics in 2008, pregnant women gave birth to babies with higher birth weights than those with child before and after the athletic event.

According to David Rich, Sc.D., M.P.H., the study's lead author, the results of their research demonstrate a connection between air pollution levels and birth weights in children. However, he also added that the findings showed that the connection may be reversed.

In 2008, for the Olympic Games and the Paralympics, the Chinese government implemented a number of aggressive measures tackling the poor air quality in Beijing, including restrictions on truck use, ceasing construction projects, halting operations in factories and seeding clouds to make it rain.

These measures dramatically reduced particulate concentration and gaseous pollution in the air for up to seven weeks during the Olympics, including a drop of 43 percent in nitrogen dioxide, 48 percent in carbon monoxide and 60 percent in sulfur dioxide, as well as a reduction in particles less than 2.5 microns wide in size.

For the study, the researchers examined information from 83,672 term births in Beijing. Birth weights were compared between mothers at the eighth month of their pregnancy during the time of the Olympics in 2008 and the same time in 2007 and 2009. Researchers found that those born in 2008 were heavier by 23 grams at birth than babies born in 2007 and 2009.

The latter months of a pregnancy are crucial to fetal development because this is the period when the fetus undergoes the most growth. Based on the results of the study, it is suggested that air pollution is interfering with the last phases of development for fetuses.

Researchers have not narrowed down yet the exact way air pollution causes lower birth weights but they speculate that factors that could've been affected by exposure include changes in the placenta's functions, reduced nutrient delivery and maternal inflammation, all of which may have a hand in impeding the growth of a baby.

Junfeng Zhang, Vanessa Assibey-Mensah, Xiaoli Duan, Tracey Woodruff, Pamela Ohman-Strickland, Barry Weinberger, Cathleen Kane, Ying Pan, Timothy Stevens, Sally Thurston, Jinliang Zhang and Kaibo Liu also contributed to the study, which received funding support from the National Institute of Environmental Health Sciences.

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