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 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.
The current study offers fresh evidence of the harmful effects of PM
1, which makes up about 80 percent of PM 2.5. Compared to larger
particles, PM 1 has a higher surface area to mass ratio and can
reach alveoli, the tiny air sacs in the lungs, Ma and colleagues
write. Ma didn’t respond to requests for comment.
Women living in the Beijing, Tianjin, and Hebei regions, the Yangtze
River delta, the Sichuan Basin, and the Pearl River delta were
exposed to PM 1 levels greater than 52.7 ug/m3 over their entire
pregnancy, the study found.
For every 10 ug/m3 increase in PM 1 exposure levels throughout their
pregnancy, women were 20 percent more likely to have very preterm
births, with babies arriving between 28 and 31 weeks gestation, and
29 percent more likely to have extremely premature babies, with
infants delivered between 20 and 27 weeks.
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Pregnancy normally lasts about 40 weeks, and babies born after 37
weeks are considered full term.
In the weeks immediately after birth, preemies often have difficulty
breathing and digesting food. They can also encounter longer-term
challenges such as impaired vision, hearing and cognitive skills, as
well as social and behavioral problems.
One limitation of the study is its reliance on satellite data to
estimate mothers’ exposure to air pollution, a method that might not
always reflect women’s actual exposure because it can’t account for
the quality of air indoors, at work, or during commutes.
Still, pregnant women should take precautions to limit their
exposure to air pollution, whether by reducing their time outdoors
during high-traffic hours or wearing an air filtration mask, advised
Dr. Shruthi Mahalingaiah, an environmental health researcher at
Boston University Medical Campus who wasn’t involved in the study.
Women considering pregnancy might also ask their doctor whether
taking baby aspirin or progesterone might help reduce their risk of
a preterm delivery, Mahalingaiah said by email.
Because the link between air pollution and preterm births may be
stronger when women are overweight or obese, mothers might also help
reduce their risk of a preterm birth by maintaining a healthy
weight, eating well and exercising, said Ryan Allen, an
environmental health researcher at Simon Fraser University in
British Columbia.
“Poor health can actually increase susceptibility to air pollution’s
effects,” Allen said by email.
SOURCE: http://bit.ly/2GaQhRC JAMA Pediatrics, online January 2,
2018.
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