Smoking during pregnancy may raise the risk of women having hyperactive preschoolers who can't pay attention.

Smoking during pregnancy has often been associated with risk of behaviour problems in children. To further explore the ties between smoking in pregnancy and behaviour and attention problems in school going children, researchers studied more than 13,000 three years old boys and girls.  The researchers took into account factors like family economic status, education level of parents, ethnicity, parents' marital status, financial difficulties and maternal smoking, drinking or drug use.

Parents were asked questions about their children to assess behaviour and hyperactivity-inattention problems such as how easily their child was distracted or if their child was prone to temper tantrums, fight with or bully other kids, argue with grownups, steal, lie, and/or cheat.

Nearly 10 percent of women reported smoking heavily (more than 10 cigarettes a day) throughout their pregnancy, 12 percent were light smokers (less than 10 cigarettes a day), and an equal percentage tried to quit. Even though no ill-effects of heavy maternal smoking during pregnancy were recorded for most boys (60 percent) and girls (70 percent), the risk of developing behaviour or attention problems increased with maternal prenatal smoking.

It was also found that the effect of smoking during pregnancy was different in boys and girls. Boys exposed to cigarette smoke in the womb were more likely to have behaviour and attention deficit problems, while girls with this exposure were more likely to experience behaviour problems alone.

Girls whose mothers quit smoking during pregnancy had a lower risk of behaviour problems than girls whose mothers never smoked. The mother's ability to quit may be a characteristic of restraint and easy temperament that their children can inherit.