Teenagers are twice as likely to be hyperactive if their mothers were anxious during pregnancy and their early years, a new study has shown.

While around five per cent of youngsters usually experience some symptoms of Attention Deficit Hyperactivity Disorder (ADHD) by the age of 16, the number jumped to 11 per cent of those whose mothers suffered anxiety.

Although some anxiety is natural during pregnancy and the early years of motherhood, the researchers measured extreme symptoms such as trembling, insomnia, dizziness and sweating.

In the study around one quarter of the women tested showed medium to high anxiety.

Researchers say they cannot be sure of a causal link, but have speculated that high levels of stress hormones may have an impact on brain development.

Dr Blanca Bolea, of the University of Toronto in Canada, who conducted the study when at the University of Bristol, said: “This is the first time that a study has shown that anxiety is linked to a child’s hyperactivity in later life

“More broadly, it shows that the stresses a mother experiences can show up in her child nearly a generation later

“We’re not sure why this might happen. It could be that the children are responding to perceived anxiety in the mother, or it could be that there is some biological effect which causes this, for example stress hormones in the placenta having an effect on a developing brain.