NEW YORK (Reuters Health) - In findings certain to add to the controversy over the health risks of electromagnetic fields (EMFs) emitted by power lines and electrical appliances, two new studies suggest that women briefly exposed to very high-intensity EMFs have an increased risk of miscarriage.
The findings are preliminary, but one of the investigators told Reuters Health that women concerned about the risk may want to stand at arm's length from electrical appliances at home and work to minimize the potentially harmful effects of EMFs.
Despite the new research, however, the evidence that EMFs increase the risk of miscarriage is far from conclusive, according to a North Carolina researcher.
A variety of sources can produce EMFs, including power lines, computer monitors, microwave ovens and photocopying machines. Their relationship to health problems has been uncertain and controversial.
For example, some research has linked EMFs from power lines to a slightly increased risk of childhood leukemia, but other studies have failed to show this connection.
Only a handful of studies have examined the possible link between EMF exposure and miscarriage risk. Two reports in the 1980s found that using an electric blanket could increase the risk of miscarriage, but the results of more recent studies have been mixed.
Problems with the way previous studies have been conducted may help explain the conflicting results, Dr. De-Kun Li of the Kaiser Foundation Research Institute in Oakland, California, told Reuters Health in an interview. Li is the author of one of two studies on the association between EMFs and miscarriage that are published in the January issue of the journal Epidemiology.
In that study, Li and his colleagues tried to address some of the flaws of previous research. Instead of looking back at a woman's exposure to EMFs after she had had a miscarriage, the researchers followed nearly 1,000 women beginning in early pregnancy.
Li said he and his colleagues used a better method of measuring EMFs -- a tracking device worn on the body for 24 hours -- than previous studies.
``Our measurement more accurately reflected the true exposure women
get in real life,'' he said.
In Li's study, a woman's average level of EMF exposure did not seem to have an effect on her risk of miscarriage.
But the researchers did detect a connection when they looked at the highest level of EMFs that women were exposed to during the day. Women with a peak EMF exposure of 16 milligauss -- much more intense than what most electrical appliances emit -- were 80% more likely to have a miscarriage than women with lower peak exposures. This risk ``barely changed'' after the researchers accounted for about 30 known miscarriage risk factors.
This risk was highest during the first 10 weeks of pregnancy and it was more pronounced in women with a history of miscarriage or problems becoming pregnant.
The investigators also found that the link between peak EMF exposure and the risk of miscarriage was stronger in women who engaged in their typical daily activities on the day they wore the EMF monitor, meaning the measurements were more likely to reflect their actual exposure.
Once Li and his colleagues arrived at their findings, another set of researchers led by Dr. Raymond R. Neutra of the California Department of Health Services in Oakland re-analyzed data they had collected previously. Their analysis also determined that women with high peak EMF exposures had an increased risk of miscarriage.
Li cautioned that the results of the studies are preliminary, and need to be confirmed. In the meantime, he said, ``It would be prudent for pregnant women or women who are planning to get pregnant to take some simple steps to avoid unnecessary exposure to magnetic fields.''
Common household sources of EMFs include microwave ovens, electric can openers, vacuum cleaners, hair dryers, electric fans, washing machines and dishwashers. Fluorescent desk lamps, electric office equipment and electrically powered public transit systems also may emit EMFs.
Completely avoiding all EMF sources is impossible, but Li said, ``The intensity of magnetic fields drops dramatically with increasing distance from the source.'' For instance, people can drastically reduce EMF exposure by standing 4 or 5 feet away from a microwave while it is on, Li said.
But in an editorial that accompanies the studies, Dr. David A. Savitz of the University of North Carolina School of Public Health in Chapel Hill writes that the studies add ``only slightly'' to the evidence supporting a link between EMF exposure and an increased risk of miscarriage.
The findings may stem in part from ``behavioral differences between women with healthy pregnancies and women who either experienced a miscarriage or were destined to have one,'' according to Savitz.
He notes that in Neutra's study, women's exposure was measured at 30 weeks' gestation -- or several months after miscarriage for the women who had lost their pregnancies. Women this far along in pregnancy tend to be less mobile than non-pregnant women. So the women who had already miscarried would probably be more mobile, and thus more likely to be exposed to EMFs at home, work and other places, Savitz suggests.
In Li's study, the North Carolina researcher points out that women's mobility may also play a role. He notes that women who miscarry are less likely to experience frequent nausea during early pregnancy.
``All other things being equal, a woman experiencing nausea will be less likely to move around her home or workplace or community, and therefore less likely to experience the diverse magnetic field sources in those places,'' Savitz writes.
So women who have less nausea, who are predisposed to have a miscarriage, might be exposed to higher peaks in EMFs in their daily life, he suggests.
But according to Li, his colleagues accounted for nausea, and it did not have an effect on the relationship between EMF exposure and the risk of miscarriage.
And Neutra told Reuters Health that women in his study were just as likely to experience bursts of high magnetic fields at 12 weeks of pregnancy as at 30 weeks.
However, Savitz believes the evidence is too slim to warrant any change in women's behavior or public policy. ``In my view, the evidence linking magnetic fields to miscarriage is very weak, below the level at which any sort of policy or behavior change would be well justified,'' he told Reuters Health.
``Given the unusual measures of magnetic fields of concern here, brief exposure to high fields or variability in fields over time, it's very unclear what someone could do to reduce exposure even if they were motivated,'' Savitz added.
SOURCE: Epidemiology 2002;13:1-3, 9-20, 21-31.
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