Research published in the British Journal of Obstetrics and Gynaecology, (2006;113:935-941 2006;113:935-941) studied data on more than 28,000 births in Brisbane, Australia and calculated the expectant mothers’ exposure to air pollution, including ozone, nitrogen dioxide and particulate matter (PM10) during the first trimester and the last trimester of the pregnancy.

During the study, 5.6% of the births occurred with less than 37 weeks gestation (the standard investigators used to define preterm births). More babies were born prematurely during the winter. High ozone exposure was associated with a 26% increase in preterm births. Increased exposure to PM10 during the first trimester was associated with a 15% increase in preterm births.