• Animal studies conducted by Nurkiewicz et al. (2004, 2006, 2011) demonstrated that exposure to (ultrafine) particulate matter induced oxidative stress that led to eNOS (endothelial nitric oxide synthase) uncoupling and reduced bioavailability of the vasodilator NO (nitric oxide).

• The daily average values of ozone (O3), nitrogen dioxide (NO2), particulate matter with an aerodynamic diameter less than 2.5 m (PM2.5), and sulfur dioxide (SO2) were calculated by averaging over all the stations within 35 km of each patients postal code centroid.

• We estimated maternal residential exposure to nitrogen dioxide (NO2), particulate matter (PM2.5) and soot during pregnancy (entire pregnancy, 1st trimester, and last month) for 3853 singleton births within the Dutch PIAMA prospective birth cohort study by means of temporally adjusted land-use regression models.