New York, Sep 8 (IANS): Women who smoke during pregnancy may increase the risk of children developing neuropsychiatric disorders associated with behavioural problems, warn researchers.

The link seems especially strong for complex presentations of the Tourette syndrome -- a nervous system disorder involving repetitive movements or unwanted sounds -- in which two or more psychiatric disorders like chronic tic disorders and pediatric obsessive-compulsive disorder (OCD) are present, the study said.

The researchers found that heavy maternal smoking (10 or more cigarettes a day) during pregnancy caused a 66 per cent increase in the risk for chronic tic disorders in the child.

"Our study not only shows an important role for maternal prenatal smoking in risk for both simple and complex chronic tic disorders in children, but it also suggests that smoking may be exerting some of its effects through subtle changes in brain development that might occur as a result of foetal exposure to nicotine," said Dorothy Grice, Professor at the Icahn School of Medicine at Mount Sinai, New York, US.

Further, heavy smoking when pregnant has been associated with a two to three-fold increased risk of several behavioural manifestations in children, including neuropsychiatric difficulties such as chronic tic disorders and attention-deficit/hyperactivity disorder (ADHD).

Maternal smoking can also lead to lower birth weight and premature delivery in children, which may, in turn, become a risk factor for subsequent behavioural problems in the child.

Furthermore, parental smoking is associated with lower socio-economic status and higher rates of alcohol and substance use, and these factors are also linked to behavioural changes in children.

"Identifying environmental causes for chronic tic disorders and related psychiatric conditions is important because if we know specific risk factors, we can develop more effective strategies for prevention," Grice added.

For the study, the team looked at data from 73,073 pregnancies, focusing on maternal smoking (including light versus heavy smoking) and children presenting with chronic tic disorders or pediatric OCD.

The team also adjusted for factors associated with maternal smoking, including maternal age, presence of maternal psychiatric disorders, socioeconomic status, consumption of beer, wine, spirits, coffee, and hashish during pregnancy, gestational age and birth weight, as well as partner smoking.

The findings were published in the Journal of the American Academy of Child and Adolescent Psychiatry.