Associations Among Exposure to Wildfire Smoke In Utero and Neonatal Outcomes

Objective: To examine associations between prenatal wildfire smoke exposure and neonatal outcomes.

Design: Population-based retrospective analysis.

Setting: Washington State.

Participants: Data from 526,649 live births between 2010 and 2018.

Methods: We used pooled cross-sectional birth records data with computed number of wildfire smoke days to examine effects of prenatal exposure on gestational age at birth, birth weight, Apgar scores, and NICU admissions using regression analysis.

Results: We found small increases in gestational age with wildfire smoke exposure in trimester 1 (B = 0.003, 95% CI [.003, .004], p < .001), trimester 3 (B = 0.011, 95% CI [.011, .012], p < .001), and across pregnancy (B = 0.003, 95% CI [.003, .004], p < .001), and a small decrease in trimester 2 (B = -0.002, 95% CI [-.002, .002], p < .001). We observed small increases in birth weight with exposure in trimester 2 (B = 0.303, 95% CI [.201, .405], p < .001) and across pregnancy (B = 0.148, 95% CI = [.086, .210], p < .001). No differences were found for Apgar scores. Finally, we found a 0.003% increase in NICU admissions with exposure in trimesters 1 and 2 (OR = 1.00, 95% CI [1.002, 1.004], [1.001,1.004], respectively) and a 0.002% increase with exposure across pregnancy (OR = 1.002, 95% CI [1.001, 1.003]).

Conclusion: Prenatal exposure to wildfire smoke had limited effects on neonatal outcomes. Although associations with gestational age and birth weight aligned with prior studies, our findings were not clinically meaningful.