Smoking during pregnancy raises the risk of the baby developing schizophrenia in later life

Mothers-to-be who smoke during pregnancy increase the risk of their children developing schizophrenia, a study has revealed.

Researchers found that the more women were exposed to nicotine the greater chance they had of having a child affected by the severe mental illness.

Signs of heavy nicotine exposure in a mother's blood were associated with a 38 per cent increased likelihood of the condition.

Scientists analysed data on 1,000 schizophrenia patients and matched their birth and health records with those of non-affected 'control' individuals.

They assessed their smoking habits by looking at levels of a nicotine marker, cotinine, in their blood.

Based on this measurement, 20 per cent of mothers of schizophrenia patients were found to have smoked heavily while pregnant, compared with 14.7 per cent of mothers of controls.

Smoking when expecting is known to contribute to significant problems in the womb and following birth, including low birth weight and attentional difficulties.

Nicotine is known to cross the placenta easily and enter the foetal bloodstream, leading to neurodevelopmental abnormalities.

Senior researcher Professor Alan Brown, from the University of Columbia, New York, said: 'To our knowledge, this is the first biomarker-based study to show a relationship between foetal nicotine exposure and schizophrenia.'

Women participating in the study had been recruited into the Finnish Prenatal Study of Schizophrenia.

Blood tests were carried out during the first and early second trimesters (three month periods) of pregnancy.

Professor Brown said: 'These findings underscore the value of ongoing public health education on the potentially debilitating, and largely preventable, consequences that smoking may have on children over time.'

Further studies could shed light on exactly how nicotine affects a foetus' brain, he added.

'Finally, it is of interest to examine maternal cotinine in relation to bipolar disorder, autism, and other psychiatric disorders. '

In a previous study, Professor Brown and his colleagues showed that offspring of mothers who smoked while pregnant have an increased risk of bipolar disorder.

The research was published in the American Journal of Psychiatry.