Researchers said if the findings are confirmed, pregnant women may want to limit their time outdoors when air quality advisories indicate unhealthy conditions.
As a dangerous heat wave settled in from the Midwest to the East Coast Friday, researchers at the National Institutes of Health (NIH) said that infants born to women exposed to high levels of air pollution in the week before birth are more likely to be admitted to a newborn intensive care unit (NICU).
Depending on the type of pollution, chances for NICU admission increased from about 4% to as much as 147%, compared with infants whose mothers did not encounter high levels of air pollution during the week before delivery.
“Short-term exposure to most types of air pollutants may increase the risk for NICU admission,” said Pauline Mendola, PhD, of the Epidemiology Branch at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, in a statement. “If our findings are confirmed, they suggest that pregnant women may want to consider limiting their time outdoors when air quality advisories indicate unhealthy conditions.”
Researchers do not know why exposure to air pollution might increase the chances for NICU admission. They theorize, however, that pollutants increase inflammation, leading to impaired blood vessel growth, particularly in the placenta, which supplies oxygen and nutrients to the developing fetus.
Rising NICU admission rates present financial challenges, as average daily NICU costs may reach or exceed $3000, the authors said. If the results are confirmed by other studies, limiting pregnant women’s exposure to high levels of air pollutants may provide a way to reduce NICU admissions.
The study, which appeared July 12 in Annals of Epidemiology, sought to determine whether prenatal exposure to air pollution might increase the chance for NICU admission, the rates of which have been rising.
It builds on previous studies that have linked elevated levels of certain kinds of air pollutants to higher risks for gestational diabetes and pre-eclampsia, as well as research that has found that infants born to women exposed to high levels of air pollutants are at risk for preterm birth, being small for their gestational age at birth, and growing more slowly than normal in the uterus.
Other research has found that air pollution can lead to lung infections in young children.
Researchers analyzed data from the Consortium on Safe Labor, which compiled information on more than 223,000 births at 12 clinical sites in the United States from 2002 to 2008. They linked records from more than 27,000 NICU admissions to data modified from the Community Multiscale Air Quality Modeling System, which estimates environmental pollution concentrations in the United States.
They matched air quality data in the area where each birth occurred to the week before delivery, the day before delivery, and the day of delivery. They then compared these time intervals to air quality data 2 weeks before delivery and 2 weeks after delivery to identify risk of NICU admission associated with pollution levels.
The researchers also examined the odds of NICU admission associated with high concentrations of particulate matter (pollution particles) less than 2.5 microns in diameter (PM2.5).
Exposure to high concentrations of organic compounds in the air was associated with a 147% increase in risk of NICU admission. Elemental carbon and ammonium ions presented similar increases in risk (38% and 39%, respectively), whereas exposure to nitrate compounds was associated with a 16% higher risk of NICU admission.
Chances of NICU admission increased significantly with exposures to traffic-related pollutants on the day before and the day of delivery, compared with the week before delivery: 4% and 3%, respectively, for an approximately 300 parts per million (ppm) increase in carbon monoxide; 13% and 9% for an approximately 26 ppm increase in nitrogen dioxide; and 6% and 3% for an approximately 3 ppm increase in sulfur dioxide.
Seeni I, Williams A, Nobles C, Chen Z, Sherman S, Mendola P. Acute air pollution exposure and NICU admission: a case-crossover analysis [published online July 12, 2019]. Ann Epidemiol. doi: 10.1016/j.annepidem.2019.07.008.