AbstractObjectiveWe examined whether the risk of stillbirth was related to ambient air pollution in a UK population.DesignProspective case–control study.SettingForty‐one maternity units in the UK.PopulationWomen who had a stillbirth ≥28 weeks’ gestation (n = 238) and women with an ongoing pregnancy at the time of interview (n = 597).MethodsSecondary analysis of data from the Midlands and North of England Stillbirth case–control study only including participants domiciled within 20 km of fixed air pollution monitoring stations. Pollution exposure was calculated using pollution climate modelling data for NO₂, NO_x and PM_2.5. The association between air pollution exposure and stillbirth risk was assessed using multivariable logistic regression adjusting for household income, maternal body mass index (BMI), maternal smoking, Index of Multiple Deprivation quintile and household smoking and parity.Main Outcome MeasureStillbirth.ResultsThere was no association with whole pregnancy ambient air pollution exposure and stillbirth risk, but there was an association with preconceptual NO₂ exposure (adjusted odds ratio [aOR] 1.06, 95% CI 1.01–1.08 per microg/m³). Risk of stillbirth was associated with maternal smoking (aOR 2.54, 95% CI 1.38–4.71), nulliparity (aOR 2.16, 95% CI 1.55–3.00), maternal BMI (aOR 1.05, 95% CI 1.01–1.08) and placental abnormalities (aOR 4.07, 95% CI 2.57–6.43).ConclusionsLevels of ambient air pollution exposure during pregnancy in the UK, all of were beneath recommended thresholds, are not associated with an increased risk of stillbirth. Periconceptual exposure to NO₂ may be associated with increased risk but further work is required to investigate this association.