A study of hundreds of pregnant women in the Bay Area found that those who were more exposed to the type of radiation produced by cell phones, wireless networks and power lines — radiation that grows more and more common — were nearly three times as likely to miscarry.

The Kaiser Permanente study, published last week in the journal Scientific Reports, did not show definitively what was causing the higher rate of pregnancy loss, nor did it isolate the potential impact of cell phones or other producers of electromagnetic fields, or EMFs.

But the authors said the results underscore the need for more research.

“EMFs have been very controversial because from a public health point of view, everybody is exposed,” said lead investigator De-Kun Li, a reproductive and perinatal epidemiologist for Kaiser’s research division in Oakland. “If there is any health effect, the potential impact is huge.”

Kaiser started the study by asking hundreds of pregnant women in its Bay Area network to spend 24 hours wearing an EMDEX Lite, a commercially available device made by Enertech Consultants Inc. that measures EMFs and is slightly larger than a deck of cards.

The women were asked to keep a diary of their activities during the day they were studied and were interviewed in person afterward. While 913 women took part, the main findings were based on a group of 453 women whose time spent wearing the meter was deemed to be “typical,” reflecting their usual work and leisure activities.

The results were stark. While 10.4 percent of the women in the lowest quartile of exposure miscarried, 24.2 percent of the rest of the women lost their pregnancies.

When researchers controlled for factors known to influence the risk of miscarriage — including nausea and vomiting, past history of miscarriage, alcohol use, caffeine intake, fever and infections — they determined that women who were in the three highest exposure quartiles were 2.72 times as likely to miscarry.

The rate of miscarriage reported in the general population is between 10 and 15 percent, Li said.

The link between higher exposure to EMFs and miscarriage was generally consistent, regardless of a woman’s race or education level, Li said. The study didn’t seek to explore differences in women in different types of jobs.

EMFs can be generated by electric appliances, power lines and transformers, and all sorts of wireless devices. Despite their wide footprint, Li said, the potential health impacts have been relatively understudied. Most inquiries have focused on potential long-term problems such as cancer, which can be difficult to measure.

“Everyone studies EMFs and cancer, but the problem is that cancer takes decades from exposure to development,” he said.

Joel Moskowitz, a public health researcher at UC Berkeley who has studied cell phone radiation, called the Kaiser study a “well-designed and carefully executed” contribution to research into the link between electromagnetic field exposure and risks of miscarriage.

He noted, though, that the results were limited because the study didn’t distinguish between varying sources of EMFs. It would be helpful, he said, if women knew how much of their exposure came from hair dryers or cell phones or other devices.

“It would be really useful if you could find out what kind of devices are putting out large fields,” Moskowitz said. “A limitation of this study is the lack of knowledge of what the source of those fields are.”

Links between electromagnetic field radiation and health problems have long been debated in the age of the cell phone. Some studies have suggested links between cell phones and cancer, decreased sperm count and other illnesses, but other research has found no such connection.

Cell phone manufacturers have long resisted attempts by state and local government to require warning labels, saying the evidence of risk is simply not there.

In the spring, The Chronicle reported that the California Department of Public Health had for years kept secret a set of guidelines about health risks associated with cell phone use.

On Wednesday, the same day the Kaiser study was published, the health department released updated guidelines and best practices for smartphone users.

“Although the science is still evolving, there are concerns among some public health professionals and members of the public regarding long-term, high use exposure to the energy emitted by cell phones,” agency Director Karen Smith said in a statement. “We know that simple steps, such as not keeping your phone in your pocket and moving it away from your bed at night, can help reduce exposure for both children and adults.”

Li said concerned consumers can take simple precautionary measures to reduce exposure to EMFs, such as increasing the distance between them and their devices.

“It doesn’t have to be drastic,” Li said, explaining that keeping a cell phone a few feet away from the body can dramatically reduce exposure.

Li said that while it was unlikely a single study will shift public policy, “The hope I have personally is that we will get more studies, so people are no longer dismissive about this relationship.”

Sophie Haigney is a San Francisco Chronicle staff writer. Email: sophie.haigney@sfchronicle.com Twitter: @SophieHaigney