EH-93-3 Is there a Link Between Video Display Terminal Use and Miscarriage?
              OFFICE OF EPIDEMIOLOGY AND HEALTH SURVEILLANCE
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                            HEALTH BULLETIN
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U.S. DEPARTMENT OF ENERGY                             WASHINGTON, D.C.
Issue 93-3                                                  March 1993
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  Is There A Link Between Video Display Terminal Use And Miscarriage?


A study conducted by the National Institute for Occupational Safety
and Health  reported in 1991 that the rates of live births,
miscarriages, and stillbirths among women who used video display
terminals (VDTs) in their jobs were similar to those among women
who did not use VDTs in their jobs (see Health Bulletin 91-2).  Two
recent studies addressed the same health concern (miscarriage) of
pregnant women who work with VDTs and reported different
conclusions.

The British Journal of Industrial Medicine (49:507-12, 1992)
published a study entitled "Spontaneous Abortion and Work with
Visual Display Units."  This study, conducted in England, compared
150 working women who had a miscarriage confirmed by a doctor with
297 pregnant working women who had not miscarried.  Information
about VDT use was collected by personal interviews using the same
questionnaire for both groups.  Information about other personal
characteristics related to miscarriage, such as smoking, alcohol
use, age, previous miscarriages, social class, and educational
level was also collected during the interview.  All of the women in
the study were employed at the time of interview and had the same
job for at least the three previous months.  In this study, the
amount of time spent using a VDT at work was about the same for the
women who had miscarriages and the still pregnant women.  The
authors concluded that their data showed no evidence that pregnant
women who use VDTs at work were at increased risk of having
miscarriages.

In November of 1992, the American Journal of Epidemiology
(136:1041-51, 1992) published a study entitled "Magnetic Fields of
Video Display Terminals and Spontaneous Abortion."  This study
compared VDT use during the first 3 months of pregnancy for two
groups of women in Finland.  One group included 191 working women
who had a miscarriage confirmed by a doctor, and the comparison
group included 394 working women who had a normal birth.  To be
included in the study, women who had worked for at least 60 days
during the first 3 months of pregnancy were identified from
Finlandþs medical registries covering the years 1975 to 1985.  The
comparison group was selected so that it was similar to the 
miscarriage group with respect to age and year of pregnancy. 
Information on the amount and type of VDT use was obtained from a
questionnaire mailed to both groups of women.   Information on
other factors related to miscarriage, such as pregnancy history,
use of birth control, smoking, and alcohol use was also collected. 
No actual measurements were made in the workplace; however,
specific magnetic field levels were measured in front of each type
of VDT model reported to have been used by any of the women.  The
miscarriage group spent about the same amount of time using VDTs in
their jobs as the comparison group.  However, the miscarriage group
was more likely than the comparison group to have used VDT models
with higher levels of measured magnetic fields.  The authors
concluded that exposure to specific high level magnetic fields from
VDT use in early pregnancy may be related to miscarriages, and that
studies which measure actual work exposures to magnetic fields in
the work setting are needed to confirm this finding.


Epidemiologic Note:

      In evaluating whether there is a cause and effect relationship
      between an exposure (or risk factor) and a disease, researchers
      carefully consider the following questions: 

      How strong is the relationship between the disease and the exposure?

      The larger the difference between the rate of disease in an exposed
      population compared to that in an unexposed population, the more
      likely the disease is caused by the exposure. 

      Was the relationship statistically significant?  If there were more
      cases of the disease than would be expected due to chance alone, the
      relationship is more likely to be causal. 

      Does the rate of disease increase consistently with increasing level
      of exposure?  If the relationship is a causal one, we might expect
      to see higher rates of disease among people who had higher levels of
      exposure or who were exposed for a longer time. 

      Did the exposure occur a sufficient amount of time before the
      disease developed to have been able to cause the disease?  Some
      diseases, like certain forms of cancer, take many years to develop,
      and to cause the disease the exposure must occur many years earlier.

      Do similar studies of different populations having the same exposure
      show similar results?  If the same relationship is seen in many
      studies, then it is likely that the relationship is causal.  If the
      results of studies are different, then it is difficult to make any
      interpretations regarding cause. 
 
      Are the results consistent with what we know about human biology and
      disease natural history?  If the results are consistent, then it is
      more likely that the relationship is causal. 

      Finally, researchers consider the design and limitations of the
      study.  Are there any weaknesses in the methodology that may
      influence the conclusions?  Have other factors that may also be
      related to the disease of interest been considered?  
.