Antisocial behaviour and ADHD linked to mothers' smoking during pregnancy
Aug 7, 2005 - 2:39:38 PM

Both antisocial behaviour and attention-deficit hyperactivity disorder (ADHD) symptoms in offspring are independently influenced by maternal smoking during pregnancy, a new study has found.

There is already substantial evidence that mothers' smoking during pregnancy is associated with both antisocial behaviour and symptoms of ADHD in offspring.

However, it is not clear whether smoking during pregnancy is independently associated with antisocial behaviour, or whether the association arises because antisocial behaviour and ADHD are linked to each other (there is evidence that ADHD behaves as a risk factor for subsequent antisocial behaviour).

Participants in the study were part of the Cardiff Study of All Wales and North West England Twins, a population-based twin register. At the time of the study, these twins were aged between five and 18.

Of the 2846 families who were sent questionnaires, 73% returned completed forms. A final sample of 723 monozygotic (identical) and 1173 dizygotic twin pairs were studied.

The questionnaires measured antisocial behaviour (e.g. 'often destroys own or other's belongings', 'bullies other children') and ADHD symptoms. Mothers were asked to report retrospectively how many cigarettes they smoked daily during their pregnancy.

It was found that males scored higher for both antisocial behaviour and ADHD symptoms than females. Of the 29.1% of mothers who reported smoking during pregnancy, 38.6% smoked 1-10 cigarettes per day, 55.1% 11-20 per day and 6.3% more than 20 per day.

Maternal prenatal smoking contributed small but significant amounts to the variance of ADHD and antisocial behaviour. The average scores for both antisocial behaviour and ADHD increased with the number of cigarettes smoked, and the two conditions were significantly associated with the amount of maternal smoking.

Maternal smoking during pregnancy contributed 3% to the variance of antisocial behaviour, and 2% to the variance of ADHD. Analysis of the data suggested that smoking in pregnancy has a distinct influence on each condition. The link between smoking in pregnancy and antisocial behaviour is not attributable to its association with ADHD.

The authors of the study cannot conclude with confidence that smoking during pregnancy is not a direct risk factor for both ADHD symptoms and conduct disorder in offspring. Therefore, they say, the safest clinical message is that smoking in pregnancy should be avoided.

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