People have an increased risk of schizophrenia if their mothers smoked during pregnancy, according to a study.

Smoking during pregnancy can increase the risk of a baby developing schizophrenia later in life, a study has found.

Heavy nicotine levels in the mother's blood were associated with a 38 per cent increased chance of schizophrenia, according to the findings published in the American Journal of Psychiatry.

The study evaluated nearly 1000 cases of schizophrenia and matched controls among offspring born in Finland from 1983-1998 who were ascertained from the country's national registry.

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

"We employed a nationwide sample with the highest number of schizophrenia cases to date in a study of this type."

The data included prenatal serum specimens drawn since 1983, during the first and early second trimesters, of a large national birth cohort of pregnant women.

The Finnish Hospital and Outpatient Discharge Registry was used to identify all recorded diagnoses for psychiatric hospital admissions and outpatient treatment visits.

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

The study found that 20 per cent of mothers of offspring with schizophrenia had smoked heavily while pregnant, compared with 14.7 per cent of the mothers of controls.

Nicotine can easily cross the placenta and enter the foetal bloodstream, potentially contributing to neurodevelopmental abnormalities.

"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," Prof Brown said.

"Future studies on maternal smoking and other environmental, genetic, and epigenetic factors, as well as animal models, should allow identification of the biological mechanisms responsible for these associations.

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