Children born to mothers who had high exposure to magnetic fields while pregnant may be at higher risk of developing asthma in childhood, a study claims.
US researchers found that exposure to low frequency electromagnetic fields (EMF) in the womb tripled the chances of the baby developing asthma.
Low frequency EMF includes those generated by power lines and electrical appliances such as fluorescent lights, microwave ovens, coffee grinders, hair dryers and vacuum cleaners.
However, UK experts say the study was not rigorously conducted and no firm conclusions can be drawn.
The researchers recruited 801 pregnant women living in Northern California, and used medical records to track the health of new-borns for up to 13 years.
During their pregnancy, the women wore monitors which measured their exposure to EMF over a 24 period.
Some 130, or 21 per cent, were found to have developed asthma.
Children born to the top ten per cent of mothers with the highest EMF exposure were 3.5 times more likely to develop asthma compared to children born to the bottom ten per cent of mothers with the lowest exposure, the study found.
The effect of EMF on asthma risk was even higher in children who already had known risk factors for asthma, such as having a maternal history of the disease or being a first-born child, the researchers said.
“In this study, we observed a dose-response relationship between mother’s MF level in pregnancy and the asthma risk in her offspring,” said Dr De-Kun Li, a senior research scientist at the Kaiser Permanante Division of Research in Oakland, California, who led the study.
“In other words, a higher maternal MF exposure during pregnancy led to a higher asthma risk in offspring.
“The best way to reduce your magnetic field exposure is distance. Magnetic field strength drops dramatically with increasing distance from the source.
“So pregnant women should try to limit their exposure to known MF sources and keep distance from them when they are in use,” he added.
However, the study has been criticised by some UK experts. Professor Patricia McKinney at the University of Leeds, a specialist in childhood epidemiology, said the study had “major deficiencies.”
These included measuring EMF exposure for just one day during pregnancy, which does not take into account the varying susceptibility of the foetus to EMF at different stages of pregnancy.
The study is published in the journal Archives of Pediatrics and Adolescent Medicine.