Smoking during pregnancy can increase a baby's chances of developing schizophrenia later in life, a study has shown.

Research in Finland 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% increased likelihood of schizophrenia.

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

Smoking habits were assessed by looking at levels of a nicotine marker, cotinine, in the blood.

Based on this measurement, a fifth of mothers of schizophrenia patients were found to have smoked heavily while pregnant, compared with 14.7% of mothers of controls.

Senior researcher Professor Alan Brown, from the University of Columbia in New York City, 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.