Chinese mothers who are exposed to higher levels of air pollution during pregnancy may be more likely to deliver preterm infants than women who live where the air is cleaner, a recent study suggests. Researchers examined data on more than 1.3 million healthy singleton pregnancies from 30 provinces in mainland China in 2013 and 2014. Almost 105,000 of the babies, or 8 percent, were born before 37 weeks' gestation, making them premature arrivals.
To see how air quality may have influenced the risk of a preterm delivery, researchers used mothers' home addresses to estimate their exposure to an extremely small type of fine particulate matter known as PM 1, a mixture of solid particles and liquid droplets smaller than 1 micrometer in diameter that's found in traffic exhaust and can include dust, dirt, soot, and smoke. Over their entire pregnancies, half of the women in the study were exposed to average PM 1 levels of 46 micrograms per cubic meter of air (ug/m3). For each 10 ug/m3 increase in PM 1 exposure, women had a 9 percent higher risk of a preterm delivery.
"We've long known that air pollution contributes to preterm birth," said Dr Leonardo Trasande, an environmental medicine researcher at New York University School of Medicine in New York City, who wasn't involved in the study. "What's novel in this study is the careful examination of smaller particles which are more readily inhaled," Trasande said by email.
Much of the previous research linking air pollution to preterm births has focused on what's known as PM 2.5, or fine particulate matter that's smaller than 2.5 micrometers in diameter, Xu Ma of the National Research Institute for Family Planning in Beijing and colleagues note in JAMA Pediatrics.