Scientists have published a major study which links outdoor air pollution with 2.7 million preterm births per year.
The study, which was led by a team from The Stockholm Environment Institute (SEI) at the University of York, found that in 2010, about 2.7 million preterm births globally – or 18% of all pre–term births – were associated with outdoor exposure to fine particulate matter.

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.

For the first time, scientists are able to quantify the global impact 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.

The study, published in the journal Environment International, suggest that addressing major sources of fine particulate matter (PM2.5) – from diesel vehicles, to agricultural waste–burning – could save babies’ lives and improve health outcomes.

PM2.5 is especially harmful to human health, as it can penetrate and lodge deep inside the lungs.

When a baby is born preterm (at less than 37 weeks of gestation), there is an increased risk of death or long–term physical and neurological disabilities.

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.

Chris Malley, a researcher in SEI at York and lead author, said: “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.”

The study revealed that 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 and respiratory problems.

“This study adds an important new consideration in measuring the health burden of air pollution and the benefits of mitigation measures,” Mr Malley added.

A pregnant woman’s exposure can vary greatly depending on where she lives – in a city in China or India, for instance, she might inhale more than 10 times as much pollution as she would in rural England or France.

The study did not quantify the risk in specific locations, but rather used the average ambient PM2.5 level in each country, and analysed the results by region.

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.

SEI is working to support more than 20 developing countries in Africa, Asia and Latin America to develop plans to reduce emissions leading to particulate air pollution. Dr Johan C.I. Kuylenstierna, co–author of the study and SEI’s director of policy, added: “Knowing that reducing outdoor air pollution could help reduce pre–term births provides a compelling new reason to invest in mitigation measures. 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.”