Maternal exposure to fine particulate matter from a large coal mine fire is associated with gestational diabetes mellitus: a prospective cohort study

Background: In 2014, the Hazelwood coal mine fire was an unprecedented event that resulted in a six-week period of poor air quality in the Latrobe Valley in regional Australia. We aimed to determine whether maternal exposure to fine particulate matter in coal mine fire smoke was associated with selected obstetric complications, including gestational diabetes mellitus, hypertensive disorders of pregnancy and abnormal placentation.

Methods: We defined a complete cohort of pregnant women with births >20 weeks in the Latrobe Valley from March 1, 2012-Dec 31, 2015 utilising administrative perinatal data. Average and peak fine particulate matter (PM_2.5) was assigned to residential address at delivery using a chemical transport model. Maternal, meteorological and temporal variables were included in final log-binomial regression models.

Results: 3612 singleton pregnancies were included in the analysis; 766 were exposed to the smoke event. Average maternal PM_2.5 exposure was 4.4 μg/m³ (SD 7.7; IQR 2.12). Average peak PM_2.5 exposure was 44.9 μg/m³ (SD 57.1; IQR 35.0). An interquartile range increase in peak PM_2.5 was associated with a 16% increased likelihood of gestational diabetes mellitus (95%CI 1.09, 1.22; <0.0001). Whereas, an interquartile range increase in average PM_2.5 was associated with a 7% increased likelihood of gestational diabetes mellitus (95%CI 1.03, 1.10; <0.0001). Second trimester exposure was of critical importance. No association for hypertensive disorders or abnormal placentation was observed.

Conclusion: This is the first study to examine obstetric complications relating to a discrete smoke event. These findings may guide the public health response to future similar events.