Preterm birth and term low birth weight associated with wildfire-specific PM_2.5: A cohort study in New South Wales, Australia during 2016–2019

Background: Exposure to wildfire smoke has been linked with a range of health outcomes. However, to date, evidence is limited for the association between wildfire-specific PM_2.5, a primary emission of wildfire smoke, and adverse birth outcomes. Objective: We aimed to estimate the risk and burden of preterm birth/term low birth weight, associated with maternal exposure to wildfire-specific PM_2.5. Methods: A total of 330,884 birth records with maternal information were collected from the New South Wales Australia from 2015 to 2019, covering 523 residential communities. Daily wildfire-specific PM_2.5 at a 0.25° × 0.25° (≈ 25 km × 25 km) resolution was estimated by a machine learning method combining 3-D chemical transport model (GEOS-Chem) and reanalysis meteorological data. Cox proportional hazards models were implemented to evaluate the association between wildfire-specific PM_2.5 and preterm birth/term low birth weight. Number and fraction of preterm birth/term low birth weight attributable to wildfire-specific PM_2.5 during pregnancy were calculated. Results: Per one interquartile-range rise in wildfire-specific PM_2.5 was found to be associated with 6.9% (HR: 1.069, 95% CI: 1.058–1.081) increased risk of preterm birth and 3.6% (HR: 1.036, 95% CI: 1.014–1.058) higher risk of term low birth weight. The most susceptible gestational window was the 2nd trimester for preterm birth whereas the 1st for term low birth weight. We estimated that 14.30% preterm births and 8.04% term low birth weight cases were attributable to maternal exposure to wildfire-specific PM_2.5 during the whole pregnancy. Male infants and mothers aged ≥ 40, experiencing temperature extremes or living in the inner region, and concepted during spring had higher risks of preterm birth/term low birth weight associated with wildfire-specific PM_2.5. Comparatively, mothers with advanced age have a higher risk of preterm birth while younger mothers were more likely to deliver term newborns with low birth weight, when being exposed to wildfire-specific PM_2.5. Pregnancy-induced hypertension enhanced the risk of preterm birth associated with wildfire-specific PM_2.5. Conclusions: This study strengthened robust evidence on the enhanced risk of preterm birth/term low birth weight associated with maternal exposure to wildfire-specific PM_2.5. In light of higher frequency and intensity of wildfire occurrences globally, more special attention should be paid to pregnant women by policy makers.