smoking during pregnancy
Smoking during pregnancy was linked to a higher risk of schizophrenia in children Daniel Berehulak/Getty Images

Mothers who smoke while pregnant are at higher risk of giving birth to a schizophrenic child. Though the odds appear greater for women who smoke a lot, the scientists suggest that any amount of smoking during gestation can have an adverse effect on the offspring's health.

The study, published in the American Journal of Psychiatry, is the first to investigate the link between a maternal smoking bio-marker known as cotinine and schizophrenia.

Cotinine is considered to be the most reliable biomarker of smoking during pregnancy. Unlike nicotine, which quickly gets degraded, it can be identified in smokers days after they have had a cigarette.

It is also more reliable than relying on mothers' self-reporting of smoking levels, because they are often unwilling to say how much they smoke, or underestimate the quantity.

38% risk increase

In the research, the scientists collected data in Finland for a population case-control study among all live births which took place in the country, between 1983 and 1998.

In total, 977 cases and 977 matched controls of schizophrenia were identified. The researchers measured cotinine levels in maternal serum collected during a blood test between the end of their first trimester and mid-second trimester of pregnancy, and archived in a biobank.

Mothers' smoking and higher maternal cotinine levels were associated with greater risks of schizophrenia in offspring. In particular, the researchers showed that foetuses who had been heavily exposed to nicotine during pregnancy – with mothers displaying levels of cotinine greater than 50 nanograms/millimetre of serum – were at 38% more risk of schizophrenia. However, even "moderate" levels of smoking was associated with risk of developing this psychiatric disease.

"Our results suggest that the more a mother smokes, the greater her risk of her child developing schizophrenia. However, the bottom line is that there is no 'safe' amount of smoking for pregnant mothers", lead author Alan Brown, from the University of Columbia, told IBTimes UK.

The risk persists despite controlling for factors such as mothers' age, history of mental disorders or socio-economic status.

Though further research is needed to confirm these findings, the study's authors believe it presents real evidence for the need to help mothers decrease or eliminate smoking during pregnancy, in order to reduce the probability of having a child affected by schizophrenia.