(CBS) – In most American cities, air pollution from cars and factories is a fact of life. But a new study raises a red flag for pregnant women by suggesting that higher levels of air pollution can pose a serious health threat even inside the womb.

“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, of the Johns Hopkins Bloomberg School of Public Health, told CBS News.

In fact, babies exposed to higher air pollution in the final trimester were 61 percent more likely to have elevated blood pressure as they grow up, the study found.

For the study, researchers looked at nearly 1,300 mothers and their babies from the Boston area. They measured the children’s blood pressure at each doctor’s appointment from the ages of 3 to 9.

And the problem doesn’t end with childhood, Mueller said.

“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,” Mueller said.

The study, published in the American Heart Association’s journal Hypertension, does not suggest that women pick up and move to less polluted areas, but rather take sensible precautions.

“If they are exercising during the third trimester of pregnancy they may want to consider not exercising outside in highly polluted areas,” Mueller said.

He also called for the government to take further steps to combat pollution. “We need regulations to keep our air clean, not only for the health of our planet but also for the health of our children,” Mueller said.

The authors note that the study has only shown an association between air pollution and high blood pressure in children and does not prove a cause-and-effect relationship. However, they say their study warrants further research to substantiate their findings.