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Impact of London's road traffic air and noise pollution on birth weight: retrospective population based cohort study

BMJ 2017; 359 doi: (Published 05 December 2017) Cite this as: BMJ 2017;359:j5299
  1. Rachel B Smith, research associate12,
  2. Daniela Fecht, research fellow3,
  3. John Gulliver, senior lecturer1,
  4. Sean D Beevers, senior lecturer4,
  5. David Dajnak, deputy manager4,
  6. Marta Blangiardo, senior lecturer1,
  7. Rebecca E Ghosh, research associate3,
  8. Anna L Hansell, assistant director23,
  9. Frank J Kelly, professor24,
  10. H Ross Anderson, emeritus professor45,
  11. Mireille B Toledano, reader12
  1. 1MRC-PHE Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, St Mary’s Campus, Norfolk Place, London W2 1PG, UK
  2. 2NIHR HPRU in Health Impact of Environmental Hazards, King's College London, London, UK
  3. 3UK Small Area Health Statistics Unit, MRC-PHE Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, London, UK
  4. 4MRC-PHE Centre for Environment and Health, Environmental Research Group, Faculty of Life Sciences and Medicine, King's College London, London, UK
  5. 5Population Health Research Institute, St George’s, University of London, London, UK
  1. Correspondence to: M B Toledano m.toledano{at}
  • Accepted 1 November 2017


Objective To investigate the relation between exposure to both air and noise pollution from road traffic and birth weight outcomes.

Design Retrospective population based cohort study.

Setting Greater London and surrounding counties up to the M25 motorway (2317 km2), UK, from 2006 to 2010.

Participants 540 365 singleton term live births.

Main outcome measures Term low birth weight (LBW), small for gestational age (SGA) at term, and term birth weight.

Results Average air pollutant exposures across pregnancy were 41 μg/m3 nitrogen dioxide (NO2), 73 μg/m3 nitrogen oxides (NOx), 14 μg/m3 particulate matter with aerodynamic diameter <2.5 μm (PM2.5), 23 μg/m3 particulate matter with aerodynamic diameter <10 μm (PM10), and 32 μg/m3 ozone (O3). Average daytime (LAeq,16hr) and night-time (Lnight) road traffic A-weighted noise levels were 58 dB and 53 dB respectively. Interquartile range increases in NO2, NOx, PM2.5, PM10, and source specific PM2.5 from traffic exhaust (PM2.5 traffic exhaust) and traffic non-exhaust (brake or tyre wear and resuspension) (PM2.5 traffic non-exhaust) were associated with 2% to 6% increased odds of term LBW, and 1% to 3% increased odds of term SGA. Air pollutant associations were robust to adjustment for road traffic noise. Trends of decreasing birth weight across increasing road traffic noise categories were observed, but were strongly attenuated when adjusted for primary traffic related air pollutants. Only PM2.5 traffic exhaust and PM2.5 were consistently associated with increased risk of term LBW after adjustment for each of the other air pollutants. It was estimated that 3% of term LBW cases in London are directly attributable to residential exposure to PM2.5>13.8 μg/m3during pregnancy.

Conclusions The findings suggest that air pollution from road traffic in London is adversely affecting fetal growth. The results suggest little evidence for an independent exposure-response effect of traffic related noise on birth weight outcomes.


  • Contributors: MBT, JG, HRA, SDB, and FJK contributed to study conception and design. DF, JG, SDB, DD, HRA, and FJK contributed to exposure assessment. REG, DF, and ALH acquired health and confounder data. RBS contributed to study design, wrote the statistical analysis plan, conducted the data analyses, and drafted the initial report. MBT contributed to the statistical analysis plan, the data analyses, and initial drafting of the report. MB contributed to the study design and statistical analysis plan. All authors contributed to interpreting the analyses and critically revising the article, approved the final draft, and agree to be accountable for all aspects of the work. All authors had full access to all of the data in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. MBT is the guarantor.

  • Funding: This work was funded by the UK Natural Environment Research Council, Medical Research Council (MRC), Economic and Social Research Council, Department of Environment, Food and Rural Affairs, and Department of Health (DH) (NE/I00789X/1, NE/I008039/1) through the cross research council Environmental Exposures & Health Initiative. The research was part funded by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Health Impact of Environmental Hazards at King’s College London in partnership with Public Health England (PHE). The work of the UK SAHSU is funded by PHE as part of the MRC-PHE Centre for Environment and Health, funded also by the UK MRC (MR/L01341X/1). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, PHE, or DH. The funders had no role in the study design; collection, analysis, and interpretation of data; writing of the report; or decision to submit the article for publication.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organisation for the submitted work other than those detailed above; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The study used SAHSU data (UK National Births and Stillbirth register data and NHS Numbers for Babies (NN4B)), supplied by the Office for National Statistics. The study was covered by national research ethics approval from the London-South East Research Ethics Committee (reference 17/LO/0846). Data access was covered by the Health Research Authority Confidentiality Advisory Group under Regulation 5 of the Health Service (Control of Patient Information) Regulations 2002 (reference 14/CAG/1039).

  • Data sharing: No additional data are available.

  • Transparency: The lead author, MBT, affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

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