Bushfire Smoke Exposure, Asthma and Pregnancy: The Smoke Is Yet to Clear

Background: Bushfire smoke exposure (BFSE) is associated with adverse pregnancy and neonatal outcomes; however, the specific impact of BFSE on pregnancies complicated by asthma is not well characterised. Methods: A retrospective cohort study analysed data from 22,166 pregnant women who gave birth in the Illawarra Shoalhaven region between January 2017 and December 2022. Women with asthma were identified by the ICD-10-AM code for asthma during hospital admission for birth. Exposure was defined using a fixed time-window assumption. Women were considered exposed to bushfire smoke if they experienced at least 4 weeks of their pregnancy between 25 October 2019 and 4 February 2020. Results: Prevalence of asthma in the total population was 8.31%. In the control cohort, outcomes for pregnant women with asthma were poorer than those without. Pregnant women with BFSE had increased odds of postpartum haemorrhage (OR 1.603; 95% CI 1.42–1.81), and decreased odds of gestational hypertension (OR 0.615; 95% CI 0.49–0.77), gestational diabetes mellitus (OR 0.703; 95% CI 0.63–0.79) and preterm birth (OR 0.813; 95% CI 0.67–0.98). Maternal asthma did not confound the relationship between BFSE and any of the primary study outcomes. Conclusions: This study emphasises the independent effects of asthma on pregnancy outcomes. The impact of BFSE on pregnant women with asthma remains unclear. Further research is needed to characterise the true effect of BFSE on pregnancies, uncomplicated and complicated by asthma.