Smoking during pregnancy has long been known to increase risks: of miscarriage, premature birth, low birth weight, certain birth defects and sudden infant death syndrome. Now another worry may be added to the list: schizophrenia.

A new study, published online Tuesday in the American Journal of Psychiatry, finds that heavy cigarette smoking by a pregnant woman raises the risk of her child developing the severe mental disorder by 38 percent.

The research was based on nicotine levels found in blood samples of pregnant mothers who gave birth in Finland between 1983 and 1998. A team of European and American scientists matched the samples, which were provided by Finland’s national registry, against a database of nearly 1,000 cases of schizophrenia (and controls) to find patterns.

“To our knowledge, this is the first biomarker-based study to show a relationship between fetal nicotine exposure and schizophrenia,” lead author Alan Brown of Columbia University Medical Center said in a release.

When the scientists analyzed the maternal blood serum samples for levels of cotinine, a marker of nicotine, they found that heavy smoking was associated with 20 percent of the mothers of children who had developed the disorder but only 15 percent of the mothers of controls. Both heavy and moderate nicotine exposure were associated with offspring who later suffered from schizophrenia.

Two caveats should be kept in mind: This is a correlation — as in association — study and so it doesn’t answer whether maternal smoking actually causes schizophrenia in offspring. And since smoking rates are known to be higher among people with the diagnosis, it’s possible that part of the correlation is due to a kind of self-selection. That is, might pregnant women who smoke and have their own genetic risk factors for schizophrenia be more likely to have children with schizophrenia?

Between 12 and 25 percent of pregnant women in Western countries smoke, according to the most recent statistics.

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