Research published ahead of print in the Journal of Epidemiology and Community Health reports that smoking during pregnancy considerably increases the risk of having a child with behavioral problems. This is noticeable in children as young as three years of age.

More than 14,000 mother and child pairs took part in the Millennium Cohort Study. This is a large population based study of UK children born between 2000 and 2001 from families receiving child benefit.

Mothers were categorized into light and heavy smokers, depending on how many cigarettes they smoked every day during pregnancy.

Using a validated questionnaire for three to sixteen year olds (Strengths and Difficulties Questionnaire), they were asked to grade their three year old children’s behavior. They focused particularly on behavioral problems and hyperactivity-attention deficit disorders.

Behavioral conduct problems were based on answers to questions about:
• the child’s temper
• the frequency of physical fights
• bullying of other children
• being argumentative with adults

Hyperactivity and inattention were based on answers to questions about:
• the degree of restlessness, fidgeting and squirming a child displayed
• the extent to which the child was easily distracted or their attention wandered

Almost one in ten of the mothers said they smoked heavily throughout their pregnancy; a further 12.5 percent said they smoked lightly during this period, and 12.4 percent said they stopped smoking while pregnant.

They took into account factors likely to influence the results, including the mother’s age at the child’s birth, her level of education and socioeconomic status, family stability and problematic parenting. Findings revealed that boys whose mothers smoked throughout pregnancy were significantly more likely to have behavioral problems, be hyperactive, and have low attention spans than boys whose mothers did not.

Boys whose mothers smoked heavily throughout pregnancy were almost twice as likely to display behavioral problems. In addition, the sons of light smokers (smoking fewer than ten cigarettes a day during pregnancy) were almost 80 percent more likely to have hyperactivity-attention deficit disorders.

By the time they were three years old, the daughters of both light and heavy smokers were significantly more likely to display behavioral problems than girls whose mothers did not smoke.

Interestingly, the authors say that girls whose mothers gave up during pregnancy were significantly less likely to have a combination of behavioral problems and hyperactivity-attention deficit disorders than girls whose mothers had never smoked. However, these findings were based on small numbers.

The authors suggest: “This may be because the ability to give up smoking may indicate restraint and an easy going temperament – traits that are then handed down to offspring.”

“Smoking during pregnancy may damage the developing structure and function of the fetal brain, which has already been shown to be the case in animals”, explain the authors. They add: “The fetal development of boys may also be more sensitive to this kind of chemical assault, which might explain why boys are more likely to have behavioral problems than girls.”

In closing, the authors say that “smoking may also boost the complex interactions between genetic and environmental factors, which contribute to a child’s development and behavioral patterns.”

“Smoking in pregnancy and disruptive behaviour in 3-year-old boys and girls: an analysis of the UK Millennium Cohort Study”
J Hutchinson, K E Pickett, J Green, L S Wakschlag
Online First J Epidemiol Community Health 2009
Journal of Epidemiology and Community Health

Written by Stephanie Brunner (B.A.)