London, Oct 1 : Mothers who smoke during pregnancy put their kids at greater risk of developing psychotic symptoms in their teens.

Researchers observed a 'dose-response effect', meaning that the risk of psychotic symptoms was highest in children whose mothers smoked the most heavily during pregnancy.

Stanley Zammit, psychiatrist at Cardiff University School of Medicine and lead study author, said: "In our cohort, approximately 19 percent of adolescents who were interviewed had mothers who smoked during pregnancy.

Researchers from Cardiff, Bristol, Nottingham and Warwick Universities studied 6,356 12-year-olds from the Avon Longitudinal Study of Parents and Children.

All the children completed an interview for psychotic-like symptoms such as hallucinations or delusions. Just over 11 percent of the children (734) had suspected or definite symptoms of psychosis.

Smoking during pregnancy was found to be linked with an increased risk of psychotic symptoms in children.

The study examined whether alcohol use and cannabis use during pregnancy was associated with a higher risk of psychotic symptoms.

Drinking during pregnancy was associated with increased psychotic symptoms, but only in the children of mothers who drank more than 21 units of alcohol a week in early pregnancy.

Only a few mothers in the study said they had smoked cannabis during pregnancy, and this was not found to have any significant association with psychotic symptoms.

It is estimated that 15 to 20 percent of women in Britain continue to smoke during their pregnancy, says a Cardiff release. These findings are published in the October issue of the British Journal of Psychiatry. (ians)