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Magnetic Fields during Pregnancy ... Risk of Miscarriage



The study (ref. below) is strange for a number of reason. The authors tried 

time-weighted average (TWA) but it didn't work. Then they tried another 

method and found a positive correlation the peak exposure (Maximum Magnetic 

Field = MMF) for a 24 hour period - a way to select for the women moving 

around the most during the day (selecting for unnormal pregnancies, 

discussed in a critical commentary by D. Savitz in the same issue of 

Epidemiology, Vol. 13, 2002:1-3). The authors then had a subsequent paper a 

few months later where they say (if I recall it correctly) that no selection 

bias should be expected.



The authors chose to make the analysis where they had the strongest 

statistical effect (at 1.6 microtesla some asymptotic threshold - a level 

inconsistent with most other EMF studies) - a hypothesis generating approach 

(evil tongues would say data dredging). The total number of pregnant women 

in the study (San Francisco and San Mateo Counties) was about 2729 but only 

969 were used in the final analysis - a total loss of 64.5 %. Of those 

refusing to participating (1185 subjects) 47.9 % were "too busy/not 

interested/too stressful". A selection was made for English-speaking women 

(which reminds me of my seven months in the area - that according to my 

opinion - half of the population speaks poor English or no English at all).



Note if you read the study that for Fig. 2, the MF exposure scale is not 

linear - the data point for 1.4-1.8 microtesla has been split (otherwise the 

number of subjects for the three lowest exposure levels would have been 

around 97 x 3 = 291 rather than 252 (969/10 = approx. 97)). I regraphed the 

data with a linear scale - the distribution is, not surprisingly, very 

skewed. I dislike the use of the word "dose" in the Results as there is no 

meaningful dose definition for EMF exposure at these frequencies (household 

appliances etc).



Fishing expeditions: It is strange that this way of working - first make the 

observation - and then the statistical analysis which can pass without a 

stir. Once the observation has been made (note that the authors state that 

they picked the level 1.6 microtesla) - the probability for the observation 

is 100 %. If I say that this one woman always had blooming cacti in her home 

and then died from Alzheimer's most (?) people would understand that you 

can't argue that way for a causal relationship. But for EMF it seems to be 

OK - the first powerline study (Boulder, Colorado around 1979) was also of a 

hypothesis generating kind.



I may mention that the study below caused thousands of people (mostly 

worried women) in Sweden to call car companies and ask for "safe cars" etc. 

This was after an "EMF person" had fed a scary magnetic fields&cars message 

to our sensational media.



The same, if not worse, fallout was in France three months ago. The 

following can be found in Sciences et Avenir (May 2002): "Reste qu’il est 

impossible de déterminer aujourd’hui à partir de quelle durée et pour quelle 

intensité l’exposition aux champs électromagnétiques peut être néfaste à 

long terme. «C’est comme se demander combien de cigarettes il est possible 

de fumer par jour avant de développer un cancer du poumon! », conclut le 

scientifique suédois" ( http://www.sciences-et-avenir.com/archives/ key 

words you can try are: champs, rayons, cem = EMF, fausses couches = 

miscarriages)

(//Last part: "It is like asking how many cigarettes it is possible to smoke 

per day before you get lung cancer."//). I strongly encourage any EMF 

interested Radsafer who had a year or two of French to browse through the 

articles in "Sciences et Avenir".





Please comment or correct if I got anything wrong.



My personal ideas only,



Bjorn Cedervall    bcradsafers@hotmail.com

http://www.geocities.com/bjorn_cedervall/

----

A Population-Based Prospective Cohort Study of Personal Exposure to

Magnetic Fields during Pregnancy and the Risk of Miscarriage



De-Kun Li1; Roxana Odouli1; Soora Wi1; Teresa Janevic1; Ira Golditch2; T. 

Dan Bracken3; Russell Senior3; Richard Rankin4; Richard Iriye5



>From the

1Division of Research, Kaiser Foundation Research Institute, Kaiser 

Permanente, Oakland, CA; 2Department of Obstetrics and Gynecology, Kaiser 

San Francisco, San Francisco, CA; 3T. Dan Bracken, Inc, Portland, OR; 

4Oregon Applied Research Services, Lake Oswego, OR; and

5Enertech Consultants Inc, Campbell, CA.



EPIDEMIOLOGY 2002;13:9-20





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