Washington: Infants born to women exposed to high levels of air pollution in the week before delivery are more likely to be admitted to a newborn intensive care unit (NICU), suggest the recent findings.
Depending on the type of pollution, chances for NICU admission increased from about 4 per cent to as much as 147 per cent, as compared to 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 of NICU admission. 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,” said Pauline Mendola, lead author of the study published in the Journal of ‘Annals of Epidemiology.’
Previous studies have linked elevated levels of certain kinds of air pollutants to higher risks for gestational diabetes and preeclampsia, a blood pressure disorder of pregnancy.
Earlier research has also shown that infants born to women exposed to high levels of air pollutants are at risk for preterm birth, of being small for their gestational age at birth and of growing more slowly than normal in the uterus.
Given these associations, the study authors sought to determine whether prenatal exposure to air pollution might increase the chance for NICU admission.
As part of the study, researchers analysed 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.
The researchers 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. Researchers 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.
Then they compared these time intervals to air quality data two weeks before delivery and two weeks after delivery to identify the 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). These types of particles originate from various sources, among them diesel and gasoline engines, power plants, landfills, sewage facilities, and industrial processes.
Exposure to high concentrations of organic compounds in the air was associated with a 147 per cent increase in the risk of NICU admission. Elemental carbon and ammonium ions presented similar increases in risk (38 per cent and 39 per cent, respectively), while exposure to nitrate compounds was associated with a 16 per cent 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 to the week before delivery: 4 per cent and 3 per cent respectively, for an approximately 300 parts per million (ppm) increase in carbon monoxide; 13 per cent and 9 per cent for an approximately 26 ppm increase in nitrogen dioxide; and 6 per cent and 3 per cent an approximately 3 ppm increase in sulfur dioxide.
Researchers do not know why exposure to air pollution might increase the chances for NICU admission. They theorise, however, that pollutants increase inflammation, leading to impaired blood vessel growth, particularly in the placenta, which supplies oxygen and nutrients to the developing fetus.