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 sixweek 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 placentationmethods we defined a complete cohort of pregnant women with births 20 weeks in the latrobe valley from march 1 2012dec 31 2015 utilising administrative perinatal data average and peak fine particulate matter pm25 was assigned to residential address at delivery using a chemical transport model maternal meteorological and temporal variables were included in final logbinomial regression modelsresults 3612 singleton pregnancies were included in the analysis 766 were exposed to the smoke event average maternal pm25 exposure was 44 gm3 sd 77 iqr 212 average peak pm25 exposure was 449 gm3 sd 571 iqr 350 an interquartile range increase in peak pm25 was associated with a 16 increased likelihood of gestational diabetes mellitus 95ci 109 122 00001 whereas an interquartile range increase in average pm25 was associated with a 7 increased likelihood of gestational diabetes mellitus 95ci 103 110 00001 second trimester exposure was of critical importance no association for hypertensive disorders or abnormal placentation was observedconclusion 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