Effects of maternal exposure to ambient air pollution on adverse birth outcomes: lay summary
Published 20 November 2025
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Being born prematurely or underweight can have health consequences both immediately and throughout life. Emerging evidence that air pollution might affect birthweight, being born early, or increase the risk of stillbirth, is a potential public health concern.
In this report, the Committee on the Medical Effects of Air Pollutants (COMEAP) examined published studies and reviews that considered whether the levels of outdoor air pollution during pregnancy affects birth outcomes. We found that the published research provided some evidence that small particles (PM2.5 and PM10) and ozone (O3) in air might be linked to these effects, but we did not consider the evidence we reviewed was robust enough for government to use it as a basis for policy decisions. There was very little research on the way that air pollutants might affect pregnancy. However, some studies suggested air pollutants may interfere with how the placenta works.
One of our biggest difficulties in conducting this piece of work was that there was no recent good-quality study that combined the results of all the available studies on human populations in one analysis. We need such studies (known as systematic reviews with meta-analyses) so that we can make decisions about whether the scientific evidence is strong enough to reach a reliable conclusion.
We recommend new meta-analyses to assess the available evidence properly. We also highlight that further research is needed on the ways that air pollution may affect the outcome of a pregnancy. In this work we have focussed on risks from air pollution from outdoor sources. There are different sources and types of air pollutants indoors which will need separate evaluation.
There are other established risk factors for low birthweight, such as smoking while pregnant. To provide some perspective for our report’s findings, the risks from smoking are likely to be higher than from typical levels of outdoor air pollution in the UK.