"What we found was that air pollution exposure during the third trimester in particular was associated with higher blood pressure in children," study author Dr. Noel Mueller, from the Johns Hopkins Bloomberg School of Public Health, told CBS News.
The research by Mueller and his team, which was published last week in the journal Hypertension, studied 1,239 mothers and their children aged three to nine in the Boston area. When the children were sorted into three categories (from highest to lowest exposure to pollution in the womb), the results showed that those in the highest exposure group were 61 percent more likely to have higher blood pressure than those in the lowest exposure group.
To gauge the levels of pollution in the areas where the women lived during their third trimester, the researchers looked at readings from nearby Environmental Protection Agency monitors. The children in the "high-risk" category were exposed to levels at least twice as high as the "acceptable" amount set by the EPA.
Mueller said exposure to pollution "causes an inflammatory response that alters genetic expression and fetal growth and development, on the pathway to high blood pressure in childhood," The Independent reported. "We know that blood pressure tracks through life. Children who have elevated blood pressure in childhood have a higher probability of having hypertension later in life and cardiovascular diseases."
While the study only demonstrates a correlation between pollution and higher blood pressure and does not confirm causation, pregnant woman should be aware, researchers said.
Dr. Melissa Smarr, an assistant professor at the Department of Environmental Health in the Rollins School of Public Health at Emory University, said there are steps pregnant women can take to avoid air pollution.
"Spending a limited amount of time near major roadways or heavily trafficked areas is one way to lessen air pollution exposure," she told The Atlanta Journal-Constitution.
Mueller also suggested pregnant women can avoid exercising outdoors in areas with bad air pollution.
Local and national governments should also work towards improving air quality, Mueller added. He explained that regulations are necessary "not only for the health of our planet but also for the health of our children."
"The conceptualization and implementation of strategic initiatives to minimize air pollution can be furthered through continued partnerships between research institutions and local, state, and national government," Smarr said.
An increased risk of high blood pressure isn't something to be taken lightly, she warned.
“High blood pressure that goes untreated in childhood may increase the risk of developing high blood pressure and/or cardiovascular disease as an adult," she said. "Left untreated, high blood can adversely affect various organs in the body, ultimately reducing the overall quality of life."
According to Smarr, the research is an important contribution to the understanding of children's environmental health "as it highlights the significance of exposure to air pollution during pregnancy as it pertains to offspring health during early childhood, which has potential implications for adult health."
"I am hopeful that these findings will encourage the design of larger future studies that are able to estimate personal maternal exposure to air pollution in the context of children's blood pressure measured multiple times throughout childhood," she said.