Does ambient air pollution trigger stillbirth?

OBJECTIVE:: We previously reported an increased risk of stillbirth associated with increases in trimester-specific ambient air pollutant concentrations. Here, we consider whether sudden increase in the mean ambient air pollutant concentration immediately before delivery triggers stillbirth. METHODS:: We used New Jersey linked fetal death and hospital discharge data and hourly ambient air pollution measurements from particulate matter ≤2.5 mm (PM_2.5), carbon monoxide (CO), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) monitors across New Jersey for the years 1998-2004. For each stillbirth, we assigned the concentration of air pollutants from the closest monitoring site within 10 km of the maternal residence. Using a time-stratified case-crossover design and conditional logistic regression, we estimated the relative odds of stillbirth associated with interquartile range (IQR) increases in the mean pollutant concentrations on lag day 2 and lag days 2 through 6 before delivery, and whether these associations were modified by maternal risk factors. RESULTS:: The relative odds of stillbirth increased with IQR increases in the mean concentrations of CO (odds ratio [OR] = 1.20, 95% confidence interval [CI] = 1.05-1.37), SO₂ (OR = 1.11, 95% CI = 1.02-1.22), NO₂ (OR = 1.11, 95% CI = 0.97-1.26), and PM_2.5 (OR = 1.07, 95% CI = 0.93-1.22) 2 days before delivery. We found similar associations with increases in pollutants 2 through 6 days before delivery. These associations were not modified by maternal risk factors. CONCLUSION:: Short-term increases in ambient air pollutant concentrations immediately before delivery may trigger stillbirth.