Pregnant mothers in Denmark who regularly used mobile phones were more likely to have children with behavioural problems, according to a study released Tuesday.
The risk was higher when the kids themselves began using cell phones at a very early age, researchers reported in the Journal of Epidemiology and Community Health.
Leeka Kheifets of the University of California at Los Angeles and colleagues examined the health records of 28,000 seven-year-olds and their mothers enrolled in the Danish National Birth Cohort.
The survey, which included nearly 100,000 women between 1996 and 2002, was designed to track the long-term health of the children.
Mothers supplied detailed information about their lifestyles, diet and habits during and after pregnancy, including cell phone use.
When their kids reached the age of seven, moms were again quizzed on their own and their children's health and behaviour.
The researchers found that kids who had been exposed to mobile phones both before and after birth were 50 percent more likely to have behavioural problems.
The findings held true even after factors that might have skewed the outcome were taken into account, they said.
Kids exposed to cell phones only while in the womb were 40 percent more likely to show abnormal behaviour, with the percentage dropping to a fifth for children whose first access to the devices occurred after they were born.
The results mirror an earlier study by the researchers of 13,000 other mothers and their kids enrolled in the same national survey.
In both groups, about three percent of the children were found to exhibit abnormal behaviour, with another three percent borderline.
The author cautioned against drawing a straight line between cell phones and difficult children, but said the findings were troublesome.
"Although it is premature to interpret these results as causal, we are concerned that early exposure to cell phones could carry a risk which, if real, would be a public health concern given the widespread use of the technology," they concluded.