The combination during pregnancy of psychological distress and exposure to air pollution can have a major impact on a child's behavioural development, a new study suggests.

US researchers monitored the progress of almost 250 pairs of mothers and their children from pregnancy through to when the children were nine years of age. Air pollution was tested throughout this period, as was the behaviour of the children.

The study found that the children of mothers who were demoralised during pregnancy tended to have more behavioural issues, such as attention problems, aggressive behaviour and rule-breaking. They were also more likely to have depression and anxiety.

The researchers defined maternal demoralisation as a measure of psychological distress that is capable of affecting a woman's ability to cope with stressful situations.

However, the study also found that the effects of this demoralisation appeared to be strongest among children whose mothers also had the highest exposure to air pollution known as PAHs.

PAHs (polycyclic aromatic hydrocarbons) are created when carbon-containing fuels, such as oil, gas and coal, are burned but the burning process is not complete. This type of pollution can be generated by motor vehicles, residential heating, tobacco smoke and coal-fired power plants.

This marks the first study to investigate the interaction between PAHs and maternal demoralisation during pregnancy and the subsequent behaviour of children.

"This study shows that the combination of physical and psychosocial stressors during foetal development magnifies the effect of each exposure. The findings are of concern because attention problems and anxiety and depression have been shown to affect peer relationships, academic performance and future wellbeing of children," the researchers commented.

They noted that the link between air pollution exposure during pregnancy and behaviour in children has previously been observed, but this latest study adds to those findings.

"The findings support policy interventions to reduce air pollution exposure in urban areas, as well as programmes to screen women early in pregnancy to identify those in need of psychological or material support," the team from Columbia University added.

Details of these findings are published in the journal, Pediatrics.

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