Non-ionizing radiation from magnetic fields is generated when common household electric devices, including electric appliances including microwave ovens, GPS systems, cell phones, television stations, baby monitors, cordless phones, garage-door openers, power lines, transformers and wireless devices, are in use.

There are two types of radiation: ionizing and non-ionizing radiation. Ionizing radiation, such as gamma rays and x-rays, carry sufficient energy to break bonds between molecules and ionize atoms. Non-ionizing radiation, on the other hand, does not have enough energy to break bonds and ionize atoms. Examples of non-ionizing radiation include extremely low frequency electromagnetic radiation, including the visible spectrum, and radio waves.

Though the dangers of being exposed to ionizing radiation are well known and include radiation sickness, cancer and genetic damage, not much is known about the health hazards of non-ionizing radiation exposure.

“Few studies have been able to accurately measure exposure to magnetic field non-ionizing radiation,” said Dr. De-Kun Li, the principal investigator of the Kaiser Permanente study published Wednesday in the Scientific Reports journal. “In addition, due to the current lack of research on this subject, we don’t know the biological threshold beyond which problems may develop, and we also don’t yet understand the possible mechanisms for increased risks.”

Pregnant women over the age 18 were asked to wear a small magnetic-field monitoring device for 24 hours. The participants were also asked to record their activities during the day and were interviewed in person by investigators to eliminate the possibility of confounding factors that could have affected the study’s results.

Researchers also controlled for other factors that increase the risk of miscarriage, including nausea/vomiting, a history of miscarriage, alcohol use, caffeine intake and maternal fever and infections.

Magnetic field measurements and pregnancy outcomes were collected for 913 women, all of whom are members of Kaiser Permanente Northern California.

“This study provides evidence from a human population that magnetic field non-ionizing radiation could have adverse biological impacts on human health,” Li said.

The study has its limitations: researchers studied miscarriages that occurred in a short time frame instead of ones that took place years later as a result of other health issues like cancer and autoimmune diseases, and participants did not carry the measuring device throughout the duration of their pregnancies. But, Li said, “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.”