Air Pollution Linked To Millions of Preterm Births Interview with:

Chris Malley PhD The Stockholm Environment Institute University of York

Dr. Chris Malley

Chris Malley PhD
The Stockholm Environment Institute
University of York What is the background for this study?

Response: When a baby is born preterm (at less than 37 weeks of gestation, an indicator of premature birth), there is an increased risk of infant death, or long-term physical and neurological disabilities. For example, 965,000 infant deaths in 2013 (35% of all neonatal deaths) have been estimated to be due to preterm birth complications. In 2010, an estimated 14.9 million births were preterm – about 4–5% of the total in some European countries, but up to 15–18% in some African and South Asian countries. The human and economic costs are enormous.

There are many risk factors for preterm birth – from the mother’s age, to illness, to poverty and other social factors. Recent research has suggested that exposure to air pollution could also be a risk factor. Our study quantifies for the first time the global impact of pregnant women’s exposure to outdoor fine particulate matter (PM2.5) by combining data about air pollution in different countries with knowledge about how exposure to different levels of air pollution is associated with preterm birth rates. What are the main findings?

Response: It finds that in 2010, about 2.7 million preterm births globally – or 18% of all preterm births – were associated with outdoor exposure to fine particulate matter (PM2.5 is especially harmful to human health, as it can penetrate deep inside the lungs). The largest contribution to global PM2.5-associated preterm births was from South Asia and East Asia, which together contributed about 75% of the global total. India alone accounted for about 1 million of the total 2.7 million global estimate, and China for about another 500,000. Western sub-Saharan Africa and the North Africa/Middle East region also had particularly high numbers, with exposures in these regions having a large contribution from desert dust. What should readers take away from your report?

Response: This study highlights that air pollution may not just harm people who are breathing the air directly – it may also seriously affect a baby in its mother’s womb. Preterm births associated with this exposure not only contribute to infant mortality, but can have life-long health effects in survivors. While many other health impacts of air pollution have been documented – most notably through the Global Burden of Disease studies – the focus has been mainly on premature deaths from heart disease, respiratory problems, etc. This study adds an important new consideration in measuring the health burden of air pollution and the benefits of mitigation measures.

Many different sources contribute to the PM2.5 problem, but in many developing countries, certain emission sources dominate. This includes emissions from cooking with biomass fuels (which is also associated with very harmful indoor pollution), diesel vehicles and other transport, and particles emitted when agricultural residues are burned in fields. It is important to realize that action needs to be taken on all the major sources. In a city, maybe only half the pollution comes from sources within the city itself – the rest will be transported there by the wind from other regions or even other countries. That means that often regional cooperation is needed to solve the problem. What recommendations do you have for future research as a result of this study?

Response: There is uncertainty in these estimates because the concentration-response function we used was based mainly on studies in the United States and Europe. Not only don’t we know whether the relationship is the same at much higher concentrations, such as those found in some Indian or Chinese cities, but the prevalence of other risk factors also varies considerably. Expectant mothers in many places are also exposed to high levels of indoor pollution from cooking smoke. Resolving these uncertainties will require more studies in these countries and regions. Is there anything else you would like to add?

Response: This study was conducted by researchers from the Stockholm Environment Institute, based in the Environment Department of the University of York, The London School of Hygiene and Tropical Medicine, and the University of Colorado. The study was funded by SEI’s Initiative on Low Emission Development Pathways, and NASA. Thank you for your contribution to the community.


Christopher S. Malley, Johan C.I. Kuylenstierna, Harry W. Vallack, Daven K. Henze, Hannah Blencowe, Mike R. Ashmore.Preterm birth associated with maternal fine particulate matter exposure: A global, regional and national assessment. Environment International, 2017; DOI: 1016/j.envint.2017.01.023

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Last Updated on February 18, 2017 by Marie Benz MD FAAD