Exposure to traffic-related air pollution during pregnancy is associated with serious neonatal complications, according to a study by UT Southwestern Medical Center researchers that matched records from more than 60,000 births with air-monitoring data.
Pregnant patients living in an urban area with elevated levels of nitrogen dioxide—one of the major components of automobile and truck exhaust—had higher rates of preterm birth, including spontaneous extremely preterm birth (born before 28 weeks), researchers found. In addition, there were increases in neonatal intensive care unit admissions, infant respiratory issues, and other adverse outcomes.
The study, which builds on earlier research at UT Southwestern, was published in the American Journal of Obstetrics & Gynecology.
“These findings suggest that air pollution from heavy traffic is a significant threat to pregnant individuals as well as to their child’s health after delivery,” says lead researcher David B. Nelson, MD, associate professor and division chief of maternal-fetal medicine in obstetrics and gynecology at UT Southwestern, in a release. “The relationship between air pollution exposure and childhood and adult respiratory conditions is well established, but this study is novel in identifying consequences to the perinatal population.”
Nelson notes that while the results demonstrate an association between air pollution levels and preterm birth, the study did not find a causal relationship.
The research involved a retrospective study of pregnancies among patients residing in the Dallas metropolitan area who gave birth at Parkland Memorial Hospital, the primary teaching hospital for UT Southwestern, between January 2013 and December 2021.
To test the association between traffic-related pollution and neonatal outcomes, average nitrogen dioxide concentrations in the area were obtained from the Environmental Protection Agency (EPA) Air Quality System database and compared with pregnancy outcomes for patients living within 10 miles of an air monitoring station.
The average exposure to nitrogen dioxide was calculated for individual pregnant patients by trimester, and regression models were used to assess the effect of pollutant exposure on gestational age at birth. Researchers also looked at indicated versus spontaneous delivery as well as neonatal outcomes while adjusting for other factors such as maternal age. More than 62,000 pregnant patients, all with exposure to nitrogen dioxide, were included.
The study found that higher levels of nitrogen dioxide exposure throughout pregnancy were significantly associated with preterm births, including spontaneous preterm births, and an increase in NICU care admissions and low birthweight infants. The researchers also found an association with higher rates of respiratory diagnosis, respiratory support, and sepsis evaluation for newborns after delivery.
When the relationship to nitrogen dioxide was evaluated for increasing severity of preterm birth, the association was highest among early preterm births. The chances for preterm birth at less than 28 weeks gestation were eight times higher for pregnancies exposed to the highest air pollution levels compared with the lowest. The data were adjusted for maternal age, self-reported race, parity, season of conception, diagnosis of diabetes mellitus, registered Health Equity Index, monitor region, and body mass index.
“It is challenging to say how much exposure to nitrogen dioxide is too much, but it’s important to note that many of the patients in our study experienced clinical impacts from exposure to nitrogen dioxide levels that were within EPA’s allowable limits,” says Nelson in the release. “Pregnant patients in urban, high-traffic areas may hold jobs or have other responsibilities that make it difficult to minimize their exposure, and they often are already at higher risk of adverse perinatal outcomes given the other social obstacles they face. These findings further highlight how the environment may impact maternal-child health.”
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