“My pregnancy was completely fine, but all of a sudden my water broke. It seemed completely random and the doctors were never able to determine any physical reason for it,” she said. “I was so careful during my pregnancy. No alcohol, no smoking and a good diet. So I’ve always wondered if it was something in the environment, not necessarily air pollution but the environment in general.”
Another Long Beach mother, Susan Taylor, said her doctor thought a gum infection most likely was the cause of her daughter, Maddy, being born early, also at 31 weeks. But, she said, “we did live near a very busy, noisy intersection.”
Like most women, Gugerty and Taylor didn't know there was a connection between air pollution and pregnancies. But Gugerty said that she “absolutely” worries about the potential health effects of the pollution around her home in Long Beach. Her son, now 12, has asthma.
About half of the babies included in the study were born in Long Beach. Air pollution experts have said that people living in that area faced a variety of increased health risks, including cancer and reduced lung function, due to heavy traffic and other sources of air pollution related to the ports and freeways.
Every year, more than half a million infants are born prematurely in the United States. In the study, 8 percent of the 81,186 babies were preterm, including 1 percent that were “very preterm,” or under 30 weeks of gestation.
The link to air pollution was strongest for the “very preterm” babies, who often weigh less than three pounds and have the greatest risk of serious health problems. The researchers compared women who lived in areas with the most traffic-related pollution with women who lived in areas with the least traffic pollution. Those in the polluted areas were 128 percent more likely to deliver “very preterm” babies.
The risk of less severe preterm babies—those born between 30 and 37 weeks--was about 30 percent higher for women living in the areas with a lot of traffic emissions.
About 3 percent of the study’s pregnant women had preeclampsia, which can result in premature babies. Its causes are unknown, although doctors think it is related to abnormal growth of the placenta.
The new study focused on “an important area of research, since there are a lot of reasons to believe that there is something happening with environmental chemicals and preeclampsia,” Woodruff said. “Women with preeclampsia have high blood pressure, and some air pollutants can increase blood pressure. This is a serious condition, and these women are at risk of adverse pregnancy outcomes.”
Scientists are uncertain how air pollutants might trigger premature babies. The chemicals may interfere with placental development, which would impair the nutrients and oxygen delivered to the fetus. Or they could trigger oxidative stress—when cells are overwhelmed and DNA is damaged by reactive compounds in the environment called free radicals.
Wu said it is likely that other pollutants are to blame, not the fine particles and nitrogen oxides. Instead, those two pollutants could be an indicator of other toxic compounds in vehicle exhaust, such as polycyclic aromatic compounds. A recent study of babies in New York City linked those compounds, called PAHs, to preterm and low-weight babies.
Wu said doctors should warn pregnant women about air pollution because “they should be aware of these issues.” While most can’t move to avoid traffic emissions, Wu said they might be able to take precautions, such as reducing their commutes or closing their windows in cars and homes.
But avoiding air pollution is virtually impossible, Woodruff said, so “pregnant women should be aware of the risks and advocate for the kinds of [government] actions that reduce overall exposure to air pollution.”