Though it's too soon to make any definitive recommendations, Adesman said pregnant women might want to take some steps to limit their exposure.
"An initial finding like this may not be sufficient grounds to make public health warnings, but common sense suggests that people may need to be mindful and society may need to be mindful of the increasing amounts of magnetic field exposure that all of us are surrounded by," Adesman said.
Barbara Grajewski, a senior epidemiologist at the U.S. Centers for Disease Control and Prevention's National Institute for Occupational Safety and Health, said the study is "intriguing" and well done in that it tracked a large number of women over time.
However, measuring EMF exposure for only one day of pregnancy may not be long enough to measure true exposure levels, and there are too few animal studies that show how EMFs impact cells to provide a biological explanation for what the researchers are observing.
It's also possible that other factors known to influence asthma risk such as socioconomic status or air pollution that researchers weren't able to account for might be playing an bigger role than EMFs, she said.
"I don't think it's a definitive, final statement that asthma and EMF are linked," said Grajewski, who has studied workplace EMF exposure.
The U.S. Centers for Disease and Control and Prevention has more on EMFs.
SOURCES: De-Kun Li, M.D., Ph.D., reproductive and perinatal epidemiologist, division of research, Kaiser Permanente, Oakland, Calif.; Jonathan Samet, M.D., professor, department of preventive medicine, and director, Institute for Global Health, University of Southern California, Los Angeles; Andrew Adesman, M.D., chief, developmental and behavioral pediatrics, Steven and Alexandra Cohen Children's Medical Center of New York, New Hyde Park, N.Y.; Barba
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