Association of Long-term Exposure to Airborne Particulate Matter of 1 μm or Less With Preterm Birth in China

What did the study find?

This study was unique in terms of its magnitude and scope. It looked at over 1.3 million pregnancies in China to determine whether there was a relationship between air pollution from very small particles (1 micrometer in size, called PM1) and preterm births. It found that pregnant women exposed to high levels of PM1 had an increased risk of a preterm birth. Specifically, where PM1 concentration was increased by 10 micrograms per cubic meter, there was a 9% increased risk of premature birth. And this risk was higher for ‘very premature’ births (28-31 weeks gestation) and ‘extreme premature’ births (20-27 weeks gestation).
Women who were particularly vulnerable to PM1 exposure were those who were older, overweight, lived in rural areas, were farmers and conceived their babies in autumn. 
 

Why does it matter?

Although the relationship between air pollution and preterm birth has been studied before, this is the first such study in the world focusing on air pollution particles at the 1 micrometer level. These particles are the size of some of the smallest bacteria and so travel deep into the lungs. But the problem is that unlike for larger air pollution particles (PM2.5 and PM10) no country has set a ‘safe’ standard for PM1. This means that regulating PM1 levels is currently impossible. 
The study also has practical implications. It suggests that pregnant women—particularly in highly polluted countries such as China and in vulnerable populations—should take measures to protect themselves from PM1 exposure. These can include limiting their exposure to indoor pollution sources such as wood fire and wearing face masks outdoors.