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.

加拿大和荷兰的一项共同研究指出，对于怀孕期间吸烟的女性，她们将承受一项风险：孩子可能会更具攻击性。研究结果已经发表在《Development and Psychopathology》杂志上。以往曾有研究证明，在妊娠期吸烟将导致婴儿出生时体重偏低，而这次的研究则指出，那些怀孕时期点着火机的母亲们，可能会提早影响她们的孩子，将额外的风险施加到他们身上，使他们更热衷于暴力行为。

另外，研究小组也发现，在吸烟的母亲中，那些家庭年收入低于4万美元的母亲们，生下具攻击性后代的可能性更大。另一项提高攻击性行为风险的因素是那些既吸烟又有反社会行为的前科的母亲们：进过局子的、高中退过学的和滥用药物的。

加拿大蒙特利尔大学的精神病学教授和圣·杰士廷医院研究中心研究员Jean Séguin与他的博士后朋友Stephan C. J. Huijbregts合作进行了该项研究。Stephan C. J. Huijbregts现在是荷兰莱顿大学的一名研究员。加拿大的拉瓦尔大学和麦吉尔大学的同事们也参与了研究。

“对于被认为有反社会行为的准妈妈们，假如她们在怀孕期间每天抽十根香烟的话，将会有67%的机会生下有肢体攻击倾向的孩子，相比之下，对于那些不抽烟或每天抽烟小于十根的妈妈们，此概率只有16%。”Séguin博士表示，“虽然这较少对外公布，但抽烟对那些几乎没有或完全没有反社会行为的母亲们而言，似乎是一个恶化的因素。”

该研究属于魁北克长期追踪研究的一部分，它是一项关于儿童的更为广泛的研究，详细调查了1745个18个月到3岁半儿童的行为。正是母亲们使她们的孩子具有了攻击性，使他们轻易对其他人进行拳打、牙咬、脚踢、干架和威吓。

导致攻击性行为的其他因素

虽然肢体攻击在学前儿童里很常见，研究人员还是确认了儿童身上与攻击性行为有关的其他产前因素：他们拥有一个不到21岁，抽烟以及强迫孩子表现规矩的母亲。研究人员同时发现，那些来自年收入不到40000美元家庭的孩子们有更大的风险具有攻击性行为。

在这种情况里，重度吸烟者有40%的机会产下具有高攻击性的后代，相比之下，轻度或非吸烟者的这一概率只有25%。而当年收入高于40000美元时，重度吸烟者和其他人两个概率的差值缩小至8%。

吸烟对后代的攻击性的影响是很大的——即使移除了如离婚、抑郁、母亲的教育和母亲怀孕年龄等其他因素。怀孕期间吸烟是阻碍降低攻击性和暴力行为风险的一个因素。

研究小组建议，那些既是烟枪又有反社会行为前科的低收入的女性应该作为产前检查的筛选标准，来决定哪些家庭需要额外的帮助去阻止攻击性行为的发展。