Non-ionising radiation from magnetic fields is produced when electric devices are in use and electricity is flowing.
It can be generated by a number of environmental sources, including electric appliances, power lines and transformers, wireless devices and wireless networks.
Humans are exposed to magnetic fields via close proximity to these sources while they are in use.
While the health hazards from ionising radiation are well-established and include radiation sickness, cancer and genetic damage, the evidence of health risks to humans from non-ionising radiation remains limited.
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Researchers asked women over age 18 with confirmed pregnancies to wear a small (a bit larger than a deck of cards) magnetic-field monitoring device for 24 hours.
Participants also kept a diary of their activities on that day, and were interviewed in person to better control for possible confounding factors, as well as how typical their activities were on the monitoring day.
Objective magnetic field measurements and pregnancy outcomes were obtained for 913 pregnant women, said Li, principal investigator of the study.
The rate of miscarriage reported in the general population is between 10 and 15 per cent, Li said.
"This study provides evidence from a human population that magnetic field non-ionising radiation could have adverse biological impacts on human health," said Li.