Professor Kate Pickett and colleagues from the University of York examined data on the smoking habits of 14,000 mothers and on the behaviour of their children.
Their analysis controlled for factors likely to influence the results, including the mother's level of education and socio-economic status, family stability and evidence of problematic parenting.
Boys whose mothers smoked heavily during pregnancy were almost twice as likely to display behavioural problems.
Daughters of smokers were significantly more likely to display behavioural problems by the time they were three years old.
What can we learn from the study?
Professor Pickett and her team believe that heavy smoking in pregnancy may be indicative of wider problems.
'Persistent and, in particular, heavy smoking throughout pregnancy may be a useful marker of families who need holistic support beyond pregnancy for a range of maternal psychosocial problems, parenting and everyday difficulties which continue to characterise these family environments three years after birth,' the researchers said.
'Such support, in addition to targeted smoking cessation interventions, may minimise associated child behaviour problems.'
What do other researchers say?
Professor Alan Maryon-Davies, president of the Faculty of Public Health, said the study added to previous work to investigate the effect of smoking on brain development.
'The assumption is that it is linked to chemicals from smoke reaching the fetus,' he said. 'But, the study raises more questions than it answers and we need to look more closely at what might be causing the behavioural changes.
'The research provides more evidence to support advising women very strongly not to smoke during pregnancy and before pregnancy,' Professor Maryon-Davies added.
'It is useful for them to realise that there may be long-term implications for their children - providing yet another reason for mothers to quit smoking before they become pregnant.'
- J Epidemiol Community Health Online 2009
- Smoking in pregnancy increases behavioural problems in three year olds.
- Heavy smoking in pregnancy may point to wider psychosocial problems.
- Supporting mothers to quit smoking before pregnancy will benefit both the mother and the child.