Babies exposed to higher levels of air pollution in the womb showed worse language and motor development at 18 months than those exposed to lower levels, according to a new King’s College London study funded by the Medical Research Council. The research, published by UK Research and Innovation on 29 April 2026, is described as the first to examine pollution exposure and development in Greater London, adding fresh evidence to concerns about the impact of traffic-related pollution during pregnancy.
First-trimester exposure emerged as the key window
The study found that pollution exposure in the first trimester of pregnancy, from conception to around week 12 or 13, was linked to poorer language skills at 18 months. Researchers reported no association with pollution exposure during the second and third trimesters. In the cohort, 498 infants from Greater London were recruited from St Thomas’ Hospital between 2015 and 2020.
Those exposed to high pollution in the first trimester scored on average five to seven points lower on language tests than babies exposed to low pollution. The children were assessed using the Bayley Scales, a standard clinical test of development that measures cognitive, language and motor skills.
Premature babies appeared more vulnerable
The findings also suggest that being born prematurely may increase the impact of pollution exposure. Among the 125 babies born prematurely, including 54 who were born before 32 weeks, those exposed to the highest pollution levels across pregnancy scored on average 11 points less than those exposed to low levels for motor skills. The researchers said they adjusted for clinical factors, including time spent on breathing support, to confirm the relationship.
Dr Alexandra Bonthrone, lead author at King’s College London, said the team wanted to determine whether air pollution levels were related to cognitive, language and motor abilities during this critical period of early childhood. She added that the first 1,000 days from conception to age two shape long-term brain health and behaviour.
What the researchers say this means for public health
The study’s senior author, Professor Serena Counsell, said maternal exposure to high levels of air traffic pollution may be associated with altered outcomes in offspring, and that reducing that exposure should be a public health priority. Professor Frank Kelly, deputy director of the MRC Centre for Environment and Health, said the results show measurable impacts on the developing brain even within what are currently considered legal air pollution limits.
Dr Bonthrone also noted that the pollution levels in the study were within the annual limits set out by the UK Government in 2010, although they were higher than the safe levels set by the World Health Organization in 2021. The pollutants analysed included particulate matter and nitrogen dioxide, both linked to traffic exhausts.
Researchers said the study forms part of wider work following children from the Developing Human Connectome Project, with the full findings published in the Journal of Physiology. The team said further follow-up will be needed to determine whether the differences seen in early life persist into later childhood.
Read the source story from UKRI: UKRI news release. For background on the MRC’s wider research mission, see About MRC.
