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A “Robust” Association“This population based cohort study with prospectively measured EMF exposure level revealed for the first time (based on our search of Medline) an increased SAB risk associated with a MMF exposure level of 16mG. The adverse MMF effect appeared to have a threshold around 16 mG and persisted regardless of the sources/locations of MMF exposure. Prenatal MMF exposure had a greater effect on early spontaneous abortion (< 10 weeks of gestation) when embryos or fetuses are much more sensitive to environmental insults, and among women who may be more susceptible to environmental exposures. The association was much stronger when women whose 24 hour MF measurements may not reflect their true prenatal MF exposure were excluded. These biologically coherent observations, all based on a priori hypotheses, provide strong evidence that prenatal MF exposure above a certain level (possibly around 16 mG) may increase SAB risk. It is also unlikely that the observed association was due to biases or unmeasured confounders, because any such biases or confounders would have to explain the above observations simultaneously. The robustness of the association against potential confounders was further supported by the evidence that, despite adjusting for more than 30 variables of known or suspected risk factors for SAB, the estimates were barely altered. Moreover, prompted by the findings in this study, Lee et al. reanalyzed the data from the study in which the findings related to TWA exposure led to funding the current study,and confirmed our observed association between MMF and SAB risk. These findings raise the question of the effect of MMF on reproductive outcomes and other health endpoints. The MMF exposure level in our study population was quite comparable to that found in a nationwide survey and our study population was racially/ethnically and socioeconomically diverse. Thus, the findings from our study should have wide implications.”
Li stressed that 16 mG is not a rare exposure. He noted that approximately 75% of his study population had at least one exposure above this threshold in a 24hour period. Li said that such peak fields are more likely to come from household electrical appliances and transportation sources than from local electrical distribution lines. The Kaiser Permanente study has cleared peer review and is scheduled to be published in the November issue of Epidemiology, Li said. His results were first disclosed at a meeting convened by the California EMF Program on April 25. Kaiser Permanente is the largest and oldest health care provider in the U.S. “It’s quite exciting if it holds up,” Dr. Nancy Wertheimer said in an interview. “ More work needs to be done on thresholds and short term high exposures.” Wertheimer, who lives in Boulder, CO, was a member of Kaiser’s internal peer review team. Wertheimer and Ed Leeper have themselves reported associations between miscarriages and EMF exposures from electrically heated beds and home electrical heating systems. Others have also seen a miscarriage risk due to magnetic fields from video display terminals (see MWN, M/J88 and M/A 92) and from power lines (see MWN, M/A92). “Taken together the EMF studies of spontaneous abortions paint a consistent picture,” said one epidemiologist, who has read the new Li paper but who asked not to be identified. The new study is the first prospective study ever done for EMF health risks and the first to use maximum magnetic field exposures to gauge risks. A total of 969 women who had been pregnant for less than ten weeks qualified for the study, and the outcomes of their pregnancies were monitored. They wore an EMDEX meter for 24 hours and were then asked if their activities during that particular day were “typical” of the pregnancy. “One of the strengths of this study was that we measured MF exposure during the relevant period and used personal measurement to capture MF exposure from all sources encountered by a woman,” Li wrote. Li found that women who were exposed to MMFs of 16 mG or more had 80% more miscarriages compared to those exposed to less than 16 mG—a statistically significant increase. But when women who said that they had worn the EMDEX on an atypical day are eliminated from the study population, the miscarriage risk increases to three times that of the less exposed women. And for pregnancies lost during the first ten weeks of gestation, the risk is close to six times that of the less exposed women. All these results are also significant. Of the 159 women who had spontaneous abortions, 132 had exposures above 16 mG, and of these 95 said that they had taken measurements on a typical day. For women who were judged to be more susceptible to environmental insults—those who had already had two or more miscarriages or who had fertility problems—the miscarriage risk is three times higher when they were exposed to 16 mG or more. This risk rises to close to five times that of the unexposed women for those pregnancies that were lost before the tenth week of gestation, a time when the fetus is most sensitive to environmental insults. Both these risks are statistically significant. “All this evidence points to an underlying biological effect of the magnetic field rather than bias or a chance finding,” Li said. “If this were a chance finding, you would not expect there to be a difference between typical and atypical exposures and between early and late abortions.” In a previous epidemiological study, Li found that women with fertility problems who used electric blankets during pregnancy had a greater chance of having babies with birth defects (see MWN, S/O95). The risk was ten times higher among women who used electric blankets during the first trimester. |
