Women who smoke during pregnancy risk delivering aggressive kids according to a new Canada-Netherlands study published in the journal Development and Psychopathology. While previous studies have shown that smoking during gestation causes low birth weight, this 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 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 research was carried out as part of a wider investigation of children, the Quebec Longitudinal Study, which examined behaviors of 1,745 children between the age of 18 months to three and a half years. Aggressive offspring were characterized by their mothers as quick to hit, bite, kick, fight and bully others.

    Other risks for aggressive behaviour

    Although physical aggression is most common in preschool children, the researchers identified other prenatal factors associated with aggressive behaviour in children: mothers who are younger than 21, who smoke and who coerce their children to behave. The researchers also found that children from families who earned less than $40,000 per year were at an increased risk for aggressive behaviour.

    In this category, heavy smokers had a 40 percent chance of having highly aggressive children, compared with 25 percent for other mothers who were moderate or non-smokers. When income was greater than $40,000 annually, the gap between heavy smokers and others fell to 8 percent.

    The effect of smoking on aggression in offspring remained significant - even when other factors were removed such as divorce, depression, maternal education and the mother's age during pregnancy. Smoking during pregnancy is one factor that could be curbed to decrease risks of aggression and violent behaviour.

    The research team recommends that low-income women, who are heavy smokers and who have a history of anti-social behaviour become a screening criterion for prenatal testing to determine what families need extra support to prevent development of aggressive behaviour. 

    加拿大和荷蘭的一項共同研究指出，對于懷孕期間吸煙的女性，她們將承受一項風險：孩子可能會更具攻擊性。研究結果已經發表在《Development and Psychopathology》雜志上。以往曾有研究證明，在妊娠期吸煙將導致嬰兒出生時體重偏低，而這次的研究則指出，那些懷孕時期點著火機的母親們，可能會提早影響她們的孩子，將額外的風險施加到他們身上，使他們更熱衷于暴力行為。

    另外，研究小組也發現，在吸煙的母親中，那些家庭年收入低于4萬美元的母親們，生下具攻擊性后代的可能性更大。另一項提高攻擊性行為風險的因素是那些既吸煙又有反社會行為的前科的母親們：進過局子的、高中退過學的和濫用藥物的。

    加拿大蒙特利爾大學的精神病學教授和圣·杰士廷醫院研究中心研究員Jean Séguin與他的博士后朋友Stephan C. J. Huijbregts合作進行了該項研究。Stephan C. J. Huijbregts現在是荷蘭萊頓大學的一名研究員。加拿大的拉瓦爾大學和麥吉爾大學的同事們也參與了研究。

    “對于被認為有反社會行為的準媽媽們，假如她們在懷孕期間每天抽十根香煙的話，將會有67%的機會生下有肢體攻擊傾向的孩子，相比之下，對于那些不抽煙或每天抽煙小于十根的媽媽們，此概率只有16%。”Séguin博士表示，“雖然這較少對外公布，但抽煙對那些幾乎沒有或完全沒有反社會行為的母親們而言，似乎是一個惡化的因素。”

    該研究屬于魁北克長期追蹤研究的一部分，它是一項關于兒童的更為廣泛的研究，詳細調查了1745個18個月到3歲半兒童的行為。正是母親們使她們的孩子具有了攻擊性，使他們輕易對其他人進行拳打、牙咬、腳踢、干架和威嚇。

    導致攻擊性行為的其他因素

    雖然肢體攻擊在學前兒童里很常見，研究人員還是確認了兒童身上與攻擊性行為有關的其他產前因素：他們擁有一個不到21歲，抽煙以及強迫孩子表現規矩的母親。研究人員同時發現，那些來自年收入不到40000美元家庭的孩子們有更大的風險具有攻擊性行為。

    在這種情況里，重度吸煙者有40%的機會產下具有高攻擊性的后代，相比之下，輕度或非吸煙者的這一概率只有25%。而當年收入高于40000美元時，重度吸煙者和其他人兩個概率的差值縮小至8%。

    吸煙對后代的攻擊性的影響是很大的——即使移除了如離婚、抑郁、母親的教育和母親懷孕年齡等其他因素。懷孕期間吸煙是阻礙降低攻擊性和暴力行為風險的一個因素。

    研究小組建議，那些既是煙槍又有反社會行為前科的低收入的女性應該作為產前檢查的篩選標準，來決定哪些家庭需要額外的幫助去阻止攻擊性行為的發展。