Pregnant women are warned to stay away from a lot of things: raw fish, alcohol, drugs — and now, traffic.
A recent study conducted at the Telethon Institute for Child Health Research in Perth, Australia, showed that increased exposure to traffic-related air pollution is associated with an up to 30 percent increase in the risk of developing preeclampsia, a serious complication in late-term pregnant women. Preeclampsia develops when blood flow is diminished during the placentation process, causing high blood pressure, swelling, pain, nausea and even seizures in the mother. Currently, the only treatment for the condition is to deliver the baby, making it the cause of many preterm births.
The researchers measured nitrogen dioxide levels at a total of 22 sites around Perth, and then used a land use regression model based on the time of year and the traffic volume to predict past levels of nitrogen dioxide in those locations. The study also collected data — including hospital and birth records — from 23,452 women who had given birth between 2001 and 2006.
Out of these 23,452 women, 4 percent developed preeclampsia, said Gavin Pereira, a postdoctoral associate at the Yale School of Medicine and lead author of the study. Those who lived closer to areas with a larger volume of traffic, such as highways, were 30 percent more likely to develop preeclampsia. Residents of congested areas who were already at a higher risk for preeclampsia, such as diabetic women, were 53 percent more likely to suffer from it than healthy women in uncongested areas.
Pereira cautioned against concluding that air pollution cased preeclampsia, the exact causes of which are remain mysterious.“This study was never going to say that preeclampsia is caused by air pollution,” Pereira said. “It’s likely that there are multiple causes and risk factors [such as obesity, and diabetes].”
Elizabeth Triche, a perinatal and environmental epidemiologist at Brown University and an expert on preeclampsia, said air pollution was almost certainly not the cause of preeclampsia but could serve as a trigger for the disorder. She said that areas with high rates of air pollution often have lower oxygen levels, which could send the mother into a hypoxic state that leaves her more vulnerable to developing preeclampsia. This effect could be particularly strong during late term pregnancy, when fast fetus growth places greater demands on its mother’s body, Triche added.
While pregnant women should stay away from prolonged exposure to traffic-related air pollution to reduce risk, the burden should not fall solely on them, Pereira said.
“The real question is how should society change,” he said. “Because the study was population-based, there should be a population-wide response: there should be a minimum distance from highways at which housing departments and schools should be built.”
Pereira said that because many researchers are working closely with government agencies such as the Environmental Protection Agency and the National Institutes of Health, societal change might be possible.
The registry data is inherently limited, said Michael Paidas, professor of obstetrics, gynecology and reproductive sciences at the Yale School of Medicine, who was not involved in the study. Incorrect diagnoses of past patients could skew the study’s results, he said.
“[There were] lots of extrapolations, but they still all seem very reasonable,” Paidas said.
Paidas also lauded the study’s efforts to address socioeconomic statuses and pre-existing conditions as well as pure medical outcomes. In hopes of better understanding preeclampsia and perhaps finding a cure, he is currently participating in a study on a cohort of pregnant Danish women.
Pereira acknowledged that the study’s methodology was not perfect. For example, he said, women could have moved locations during their pregnancy, modifying their apparent exposure to traffic-related air pollution in the hospital’s birth registry.Periera has recently started a study at Yale looking at the association between traffic related air pollution and preterm births.