Several recent studies have provided more information about the health effects of computer use, and one of them included what appears to be reassuring news about the effects of electromagnetic fields on pregnant women.
Previous studies of video display terminal use among women have yielded conflicting and inconsistent results, producing growing concern among workers and managers about the prudence of assigning women of child-bearing age to computer-related jobs.
Some studies have suggested -- but not proved -- a link between computer radiation and a variety of pregnancy problems, including miscarriage, birth defects and birth problems.
A long-awaited study by the National Institute for Occupational Safety and Health (NIOSH), published last month in the New England Journal of Medicine, analyzed the experience of women who worked as operators for the telephone company and used video terminals.
"We conclude that in this study, the use of VDT's and exposure to the electromagnetic fields they produce were not associated with an increased risk of spontaneous abortion," the NIOSH researchers reported.
The study of 2,430 women found there was "no difference in risk" among women who sat in front of a VDT for more than 25 hours a week compared with those in similar jobs who did not use video terminals.
Earlier studies had suggested that prolonged exposure to the electromagnetic fields generated by computer monitors increased the risk of health problems.
"We don't think this study answers all questions of VDTs and health, but it does answer some questions specifically related to VDT's and miscarriages," said Barbara A. Grajewski, senior epidemiologist for NIOSH in Cincinnati, where the agency is based.
She said other data from the six-year study, including the possible impact of VDT work on premature births, birth defects and birth weights, were being analyzed.
All the workers in the study, including those who were listed as non-VDT users, were exposed to extremely low frequency, or ELF, magnetic radiation, the kind associated with the power supplies of home and office electrical devices.
Ms. Grajewski said the researchers noted that ELF was present but did not reach any conclusions about it.
"We were not trying to draw any conclusions about what ELF fields would do to miscarriage rates," she said. "We just measured it because it was there."
The type of radiation more closely associated with video terminals is very low frequency, and it falls in the range of 45 kilohertz to 60 kilohertz, or 45,000 to 60,000 cycles a second.
But including the ELF data, conclusions or not, led to some complaints.
"If they had just left it at VLF I would have much less problem with the study," said Louis Slesin, editor of the New York-based newsletter VDT News, who monitors government studies from around the world about video terminals and microwave emissions.
"The inclusion of 'accompanying magnetic fields' is a conclusion based on political imperative as perceived by NIOSH." The federalagency, he said, has been under pressure to report on ELF radiation and adapted a study for a different purpose to that end.
Slesin noted that only two models of VDTs were included in the tests, one made by IBM and the other by Computer Controls Inc.
He said there were "tremendous variations" in radiation levels even among models made by the same company, but Ms. Grajewski said most terminals have similar emissions and that the terminals tested were representative of models used widely by businesses.
At IBM, a spokesman, Brian Doyle, said the NIOSH study "adds to the growing body of scientific evidence in support of our belief that desktop computers are safe."
One large corporate customer for computer monitors is Pacific Bell Co., where 55,000 employees work on terminals.
The company's medical director, Dr. Jake Moll, said he was pleased by the NIOSH study and said Pacific Bell would "continue to follow closely the ongoing research sponsored by electrical power companies and the federal government for any possible deleterious effects from exposure to electromagnetic fields."
A second study released last month, by Kimmel Gerke Associates Ltd. of New Brighton, Minn., an independent laboratory, measured the extent of protection offered by several popular models of "radiation screens," which fit over the face of a video terminal.
The study was sponsored by Optical Coating Laboratories Inc. of Santa Rosa, Calif., whose products include anti-glare filters for video terminals.
An Optical spokeswoman said the tests had been commissioned to "clear up the confusion about computer radiation."
Some companies have capitalized on the public's concern over radiation by promoting thin screens, made of glass or mesh, as effective barriers against "computer radiation."
What they do not say is that the screens are effective only against certain types of radiation.
The screens block electrical fields that cause electrostatic charges on the monitor. Static attracts dust and other airborne particles, and those pollutants, in turn, are suspected as a cause of skin rashes and eye irritation.
"Based on what is known today about the physical laws of electromagnetic radiation in the ELF/ VLF range, it is not possible to block magnetic fields with a material that you can see through," said Daryl Gerke, who conducted the testing for Kimmel Gerke Associates.