Adjusted relative risksa between criteria air pollutants and risk of asphyxia (n = 590 cases among 223,375 singleton births). Abbreviations: CO, carbon monoxide; NOx, nitrogen oxides; O3, ozone; PM10, particulate matter ≤10 microns; PM2.5, particulate matter ≥2.5 microns, SO2, sulfur dioxide.a Multipollutant models adjusted for region, marital status, parity, maternal age, maternal race, caesarean delivery, type of insurance, maternal BMI, smoking/alcohol, comorbidities (HIV, hypertension, diabetes, thyroid disease), season of conception, and asthma. Relative risks are estimated for an IQR increase in pollutants. * Denotes statistical significance at P < 0.05.