Non-ionising radiation -- radiation that produces enough energy to move around atoms in a molecule, but not enough to remove electrons completely -- 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.
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, said De-Kun Li, a reproductive and perinatal epidemiologist at the Kaiser Permanente -- a US-based health care firm.
For the study, published in the journal Scientific Reports, the team asked for 913 pregnant women over age 18 to wear a small (a bit larger than a deck of cards) magnetic-field monitoring device for 24 hours.
After controlling for multiple other factors, women who were exposed to higher magnetic fields levels had 2.72 times the risk of miscarriage than those with lower magnetic fields exposure.
The increased risk of miscarriage associated with high magnetic fields was consistently observed regardless of the sources of high magnetic fields. The association was much stronger if magnetic fields was measured on a typical day of participants' pregnancies.
The finding also demonstrated that accurate measurement of magnetic field exposure is vital for examining magnetic field health effects.
"This study provides evidence from a human population that magnetic field non-ionising radiation could have adverse biological impacts on human health," Li noted.
"We hope that the finding from this study will stimulate much-needed additional studies into the potential environmental hazards to human health, including the health of pregnant women," he said.