Prenatal wildfire smoke exposure and adverse neonatal outcomes in a high-risk cohort of pregnant women with asthma

BACKGROUND: Climate change is contributing to more frequent wildfires. Exposure to wildfire smoke during pregnancy increases the risk of adverse neonatal outcomes. Pregnant women with asthma and their newborns are particularly at risk of negative effects from wildfire smoke exposure and remain understudied. Determining critical windows of exposure during pregnancy could help inform mitigation strategies for this high-risk group. OBJECTIVE: This study aimed to assess the association of prenatal wildfire smoke exposure with adverse neonatal outcomes in mothers with asthma and to determine which period of pregnancy is most critical. STUDY DESIGN: This was a multicenter cohort study (Breathing for Life Trial) including mothers and newborns from 6 antenatal clinics across 4 cities in Australia (Sydney, Brisbane, Newcastle, Canberra). Pregnant women (n=1275) with asthma were recruited at 12 to 23 weeks of gestation. Chronic lung disease (other than asthma), miscarriages, and perinatal deaths were excluded. Prenatal wildfire smoke exposure days and daily wildfire-related particulate matter ≤2.5 μm concentrations were determined by residence. Exposure over pregnancy was assessed in 3 ways: (1) cumulative days of wildfire smoke (0, 1-4, 5-9, ≥10 days); (2) wildfire smoke-affected days and wildfire-related particulate matter ≤2.5 μm as continuous variables for each gestational month; and (3) a natural experiment comparing exposure during the 2019-2020 summer extreme wildfire period with historical controls. Neonatal outcomes included birthweight, low birthweight (<2500 g), gestational length, preterm birth (<37 weeks), neonatal intensive care unit admission, and cesarean delivery. RESULTS: ); and the median number of prenatal cumulative days of wildfire smoke exposure was 3 (range, 0-71 days). Prenatal exposure to ≥10 cumulative wildfire smoke days was associated with low birthweight (adjusted odds ratio, 4.2; 95% confidence interval, 1.2-13.9), preterm birth (adjusted odds ratio, 2.8; 95% confidence interval, 1.1-7.2), and neonatal intensive care unit admission (adjusted odds ratio, 5.0; 95% confidence interval, 1.4-17.8). Exposure to wildfire-related particulate matter ≤2.5 μm in the second and third gestational months was associated with preterm birth, small for gestational age, and neonatal intensive care unit admission. In the natural experiment, prenatal exposure was associated with low birthweight (adjusted odds ratio, 2.6; 95% confidence interval, 1.1-6.2), preterm birth (adjusted odds ratio, 2.5; 95% confidence interval, 1.2-5.2), and neonatal intensive care unit admission (adjusted odds ratio, 4.8; 95% confidence interval, 2.0-11.2). CONCLUSION: In pregnant women with asthma, prenatal exposure to wildfire smoke early in pregnancy increases the risk of adverse neonatal outcomes. Measures to reduce wildfire smoke exposure early in pregnancy could be beneficial.