Pregnant smokers may "program" their children to become smokers suggests the latest research.
Researchers based their findings on more than 3,000 mothers and their children, who were part of a long-term pregnancy study in Brisbane, Australia in 1981.
They assessed the smoking patterns of children when they reached the age of 21 in relation to the behavior of their mothers during the pregnancy.
About a third of the women said that they had smoked during their pregnancy.
The proportion of the children who took up regular smoking was greater among those whose mothers had smoked during the pregnancy than among those whose mothers had not.
Children whose mothers had smoked while pregnant were almost three times as likely to start smoking regularly at or before the age of 14 and around twice as likely to start smoking after this age as those whose mothers were non-smokers.
Smoking patterns among children whose mothers stopped smoking while pregnant, but then resumed the habit, were similar to those whose mothers had never smoked.
The findings held true even after adjusting for other factors likely to influence the results.
The authors conclude that their research provides some evidence that smoking during pregnancy has a direct effect on the child's chances of becoming a smoker. And they suggest that their findings are another reason why pregnant women should be discouraged from smoking.
This study also appears in the December 2006 issue of the British journal Tobacco Control.