Assessment of the association between ambient air pollution and stillbirth in the UK: Results from a secondary analysis of the MiNESS case–control study

Abstract

Objective: We examined whether the risk of stillbirth was related to ambient air pollution in a UK population. Design: Prospective case–control study. Setting: Forty-one maternity units in the UK. Population: Women who had a stillbirth ≥28 weeks’ gestation (n = 238) and women with an ongoing pregnancy at the time of interview (n = 597). Methods: Secondary 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, NOx and PM2.5. 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 Measure: Stillbirth. Results: There 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). Conclusions: Levels 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.