Girls whose grandmothers smoked are more likely to develop symptoms of autism, a new scientific study has claimed.

The research, published by the University of Bristol, identified the trend across a group of more than 14,500 children.

When looking at girls whose maternal grandmother smoked during pregnancy, children were 67 per cent more likely to exhibit autistic traits, such as poor social awareness.

The same was true for boys, who were 53 per cent more likely to display such behaviours if their grandmother smoked.

“We were intrigued about why autism seems to be gathering more prevalence. General smoking, particularly women’s smoking in pregnancy, came to a peak round the Second World War,” said the study’s co-author, Jean Golding.

He added that previous research in animals has shown that environmental effects, such as smoking, can be passed down through multiple generations.

Of the 14,500 participants, 7,000 were found to have autistic traits, while 177 were diagnosed with autism.

However, James Cusack, director of science for the organisation Autistica, said the study does not conclusively prove that smoking causes autism.

“The study applies careful analyses to data from a world-leading birth cohort project. But conclusions are drawn from ‘reported or possible’ autism diagnoses and ‘predictive traits’.

“Also, although confounding factors are taken into account, there may be others not considered in the analyses. Further research is needed to understand whether grandmother’s smoking during pregnancy is linked to autism in grandchildren. This study alone does not indicate a causal link.”