In the latest study, researchers took sperm from 29 men aged 26 to 45 and placed them either under a wi-fi connected laptop or away from the computer.
The laptop then uploaded and downloaded information from the internet for four hours.
At the end of the experiment, 25 per cent of the sperm under the laptop had stopped moving and 9 per cent showed DNA damage.
By comparison, just 14 per cent of samples kept away from the wi-fi stopped moving. And just 3 per cent suffered DNA damage, the journal Fertility and Sterility reports.
The wireless connection creates electromagnetic radiation (EMR) that damages semen, the scientists, from the United States and Argentina, believe.
Lead researcher Conrado Avendano, of Nascentis Medicina Reproductiva in Cordoba, said: ‘Our data suggest that the use of a laptop computer wirelessly connected to the internet and positioned near the male reproductive organs may decrease human sperm quality.
‘At present we do not know whether this effect is induced by all laptop computers connected by WiFi to the internet or what use conditions heighten this effect.’
A separate test with a laptop that was on, but not wirelessly connected, found negligible EM radiation from the machine alone.
The findings fuel concerns raised by a few other research teams.
Some have found that radiation from mobile phones creates feeble sperm in the lab, for example.
And last year urologists described how a man sitting with a laptop balanced on his knees can crank up the temperature of his scrotum to levels that aren’t good for sperm.
So between the heat and the radiation from today’s electronic devices, testicles would seem to be hard-pressed.
However, Dr Robert Oates, the president of the Society for Male Reproduction and Urology, has managed to father two kids despite having both a laptop and an iPad. He doesn’t believe laptops are a significant threat to male reproductive health.
Remarking on the new study, he said: ‘This is not real-life biology, this is a completely artificial setting.
‘It is scientifically interesting, but to me it doesn’t have any human biological relevance.’
He added that so far, no study has ever looked at whether laptop use has any influence on fertility or pregnancy outcomes.
Suddenly all of this angst is created for real-life actual persons that doesn’t have to be,’ said Oates, also of Boston Medical Center.
He added: ‘I don’t know how many people use laptops on their laps anyway.’
According to the American Urological Association, nearly one in six couples in the U.S. have trouble conceiving a baby, and about half the time the man is at the root of the problem.
While the impact of modern technology is still murky, lifestyle does matter, researchers say.
Earlier this month, a report in Fertility And Sterility showed that men who eat a diet rich in fruit and grains and low in red meat, alcohol and coffee have a better shot at getting their partner pregnant during fertility treatment.