Pregnant women who smoke could cause harm to the development of the brain of their unborn child, a study says.

U.S. Researchers noted that those whose mothers puffed more than 20 cigarettes a day were more prone to commit crime and potentially become repeat offenders as they age.

Researchers have noted that exposure to such smoke in the womb may damage developing areas of the brain that are chiefly related to the behavior of a person. About 4,000 adults between ages 33 and 40 were observed for the study, between a period of 1959 and 1966. The study is published in the Journal of Epidemiology and Community Health.

Those smoking more than 20 cigarettes a day were categorized as heavy smokers.

Researchers once again checked records of children of these smoking moms in 1999/2000, and noted that they had a 30 per cent increased chance of having committed crimes.

Dr Angela Paradis, of Harvard School of Public Health, Boston, who led the study, said it was “not possible to 'definitively' describe heavy smoking as a cause of adult criminal offending, but the results support a 'modest causal relationship'.”

Research also noted that the exposure of nicotine was the culprit.

Doctors in the UK began warning from 1971 the ill effects of smoking on an unborn baby and later launched the no smoking campaign in 1974.

“This study adds to a substantial body of evidence linking smoking in pregnancy to difficult temperament in infants, behavior problems in children, and antisocial behavior in adult offspring,” Professor Kate Pickett, Department of Health Sciences, University of York.