We used pooled cross-sectional data from birth records to examine the relationship between air quality measurements and neonatal outcomes. We computed the number of wildfire smoke days to examine the impact of in utero exposure to wildfire smoke on gestational age at birth, birth weight, Apgar scores, and NICU admissions. We analyzed the data using linear and logistic regression.

We found a small increase in gestational age at birth with exposure to wildfire smoke in trimester 1 (B = .003, 95% confidence interval [CI] [.003, .004], p < .001), trimester 3 (B = .011, 95% CI [.011, .012], p < .001), and at any point in pregnancy (B = .003, 95% CI [.003, .004], p < .001). Conversely, we found a small decrease in gestational age at birth with exposure to wildfire smoke in trimester 2 (B = –.002, 95% CI [–.002, .002], p < .001). We found minor increases in birth weight with exposure to wildfire smoke in trimester 2 (B = .303, 95% CI [.201, .405], p < .001) and at any point in pregnancy (B = .148, 95% CI = [.086, .210], p < .001). We found no statistically significant difference for 5- and 10-minute Apgar scores with in utero exposure to wildfire smoke. Finally, we found a 0.003% increase in NICU admissions with exposure to wildfire smoke in trimesters 1 and 2 (odds ratio = 1.00, 95% CI [1.002, 1.004] and [1.001, 1.004], respectively) and a 0.002% increase in NICU admission with exposure to wildfire smoke at any point during pregnancy (odds ratio = 1.002, 95% CI [1.001, 1.003]).

In utero exposure to wildfire smoke had limited effect on neonatal outcomes. Although results related to gestational age and birth weight were consistent with those in previously published literature, our findings were not clinically meaningful.