Babies exposed to high amounts of air pollution in the womb show slower developmental symptoms at 18 months than babies exposed to lower levels.
The King’s College London study is the first to examine pollution exposure and development in Greater London, measuring the language and motor skills of babies whose mothers were pregnant in the capital.
Exposure to pollution emitted from sources such as traffic during the first trimester of pregnancy (from conception to 12/13 weeks) was associated with poorer language skills at 18 months.
This research is the first to explore whether preterm birth is affected by exposure to pollution during pregnancy. The study found that pollution has an even greater impact on premature babies, with this group showing poor motor as well as language skills.
The research is based on the same group of babies whose brain structures were found to vary in size due to exposure to pollution in the womb. Lead author Dr Alexandra Bonthron, who carried out the research at the School of Biomedical Engineering and Imaging Sciences at King’s College London, said: “We wanted to establish whether air pollution levels during this critical period of childhood are related to cognitive, language and motor abilities. The first 1,000 days from conception to two years of age shape long-term brain health and behaviour.”
The study involved 498 infants from Greater London who were recruited from St Thomas’ Hospital between 2015-2020. Of the group, 125 were born prematurely, and within that group 54 were born at less than 32 weeks – known as ‘very and extremely premature’. The infants underwent a standard clinical test of development, known as the Bayley Scales, which measures cognitive, language and motor skills – with a score of 100 reflecting the population average.
Those exposed to high pollution in the first trimester of pregnancy scored an average of 5-7 points lower on language tests than infants exposed to low pollution. There was no link to pollution in the second and third trimesters.
Premature babies exposed to the highest pollution levels in the womb during pregnancy scored an average of 11 points lower on motor skills than babies exposed to the lowest levels.
Dr Bonthron said: “Although premature babies are already more likely to have difficulties with motor development, we adjusted for various clinical factors, such as time spent on support to breathe, to confirm the association between air pollution and motor development.”
King’s team collaborated with the Environmental Research Group at Imperial College London to measure the pollutants. The London Air Pollution Toolkit models pollution levels based on traffic volume and average travel speed. This helped researchers estimate how much pollution mothers were exposed to during pregnancy based on their home postcode.
Dr Bonthron said: “The levels in this study of children born in Greater London from 2015 to 2020 were within the annual limits set by the government in 2010 legislation on air quality, although they exceed safe levels set by WHO in 2021.”
The pollutants analyzed included particulate matter and nitrogen dioxide, which are emitted by traffic exhaust. Small particles of these molecules can be inhaled by humans. According to the State of Global Air report, breathing air pollution is the second biggest risk factor for death in children under 5 globally, after malnutrition.
Dr Bonthron said: “At this stage, it is too early to say whether these children will be able to catch up with their peers – the only way would be to study them later in childhood. It may be that developmental differences have an impact on learning and information processing, but we will not know for sure until we do future studies.”
Senior author Professor Serena Council, School of Biomedical Engineering and Imaging Sciences, King’s College London, said: “This work adds to a growing body of evidence that maternal exposure to high levels of air traffic pollution may be associated with altered outcomes in their offspring. Reducing maternal exposure to air traffic pollution should be a public health priority.”
Professor Frank Kelly, from the Environmental Research Group at Imperial College London, said: “This study shows that even within what we currently call ‘legal’ levels of air pollution, we are seeing measurable effects on the developing brain. This should fundamentally change the way we think about ‘acceptable’ air quality for pregnant women and young children. Improving air quality is not just about cleaner skies; it is about giving every child the best possible start in life.”
The latest study is part of a broader research of a group of children who underwent brain MRI before or shortly after birth, known as the Developing Human Connectome Project.
