Researchers at the University of California have found that using a mobile phone while pregnant could cause behavioural and emotional problems in children.
The study of more than 13,000 children found that pregnant women using the handsets just two or three times a day was enough to raise the risk of their babies developing hyperactivity and difficulties with conduct, emotions and relationships by the time they reached school age.
The likelihood is even greater if the children themselves used the phones before the age of 7.
Specifically, mothers who used mobile phones were 54 percent more likely to have children with behavioral problems.
When the children also later used the phones themselves, they were: 80 percent more likely to suffer from difficulties with behaviour.
They were also 25 percent more at risk from emotional problems, 34 percent more likely to suffer from difficulties relating to their peers,5 percent more likely to be hyperactive, and 49 percent more prone to problems with conduct.
The results of the study took the top scientists who conducted it by surprise.
The research will carry particular weight because one of its authors, UCLA's Professor Leeka Kheifets, had previously been sceptical that mobile phones could pose a risk to health.