Pregnant women who smoke risk delivering aggressive kids, according to a new Canada-Netherlands study.

Aggressive offspring were characterized by their mothers as quick to hit, bite, kick, fight and bully others. The research has been published in the journal Development and Psychopathology.

While previous studies have shown that smoking during gestation causes low birth weight, the new research shows mothers who light up during pregnancy can predispose their offspring to an additional risk: violent behaviour.

What's more, the research team found the risk of giving birth to aggressive children increases among smoking mothers whose familial income is lower than 40,000 dollars per year.

Another risk factor for aggressive behaviour in offspring was smoking mothers with a history of antisocial behaviour: run-ins with the law, high school drop-outs and illegal drug use.

Psychiatry professor and researcher Jean Séguin, of the Université de Montréal and Sainte-Justine Hospital Research Center, co-authored the study with postdoctoral fellow Stephan C. J. Huijbregts, now a researcher at Leiden University in the Netherlands, as well as colleagues from Université Laval and McGill University in Canada.

"Mothers-to-be whose lives have been marked by anti-social behaviour have a 67 percent chance to have a physically aggressive child if they smoke 10 cigarettes a day while pregnant, compared with 16 percent for those who are non-smokers or who smoke fewer than 10 cigarettes a day," says Dr. Séguin.

"Smoking also seems to be an aggravating factor, although less pronounced, in mothers whose anti-social behaviour is negligible or zero,” the expert added.

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