Does Your Computer Monitor Pose A Risk?
In the late 1970s, as the use of video display terminals (VDTs) in the workplace became increasingly common, questions arose concerning the potential effects on pregnancy outcomes of working with these terminals. Clusters of miscarriages and birth defects were reported at several workplaces in the United States and Canada.
Various VDT exposures and emissions have been measured: X-rays, ultraviolet radiation, visible light, infrared radiation, radio frequency fields, power-frequency EMFs, chemicals (PCBs), air ions, and static fields. Workers' exposures to these emissions are very low. However, unlike other office equipment, VDTs emit pulsed electromagnetic fields in the very low frequency (VLF) range, specifically 15,000 to 30,000 Hz (see the Electromagnetic Spectrum). In 1982, a laboratory in Spain reported that malformations occurred in chicken embryos exposed to pulsed magnetic fields at low frequencies. Although these results could not be repeated by the Spanish researchers or others, epidemiologic studies of workers were started to find out if miscarriages or birth defects occur more among VDT users.
In the following decade, more than 10 epidemiologic studies were completed in the United States, Canada, Sweden, Finland, Norway, and Denmark. Most of the studies reported that work with VDTs did not affect the risk of miscarriage or birth defects (Ericson and Kallen, 1986; Bryant and Love, 1989; Nielsen and Brandt, 1990). However, in only three studies were VDT exposures measured.
The U.S. government has no exposure or emission standards for magnetic fields from video display terminals (VDTs). The Swedish government issued guidelines recommending that VDTs purchased by the government produce extremely low frequency (ELF) magnetic fields of no more than 2 mG at a distance of 30 centimeters (11.8 inches) from the VDT surface. The standard is based on what is technologically achievable, not on medical or epidemiological research, according to the Swedish Board for Technical Accreditation (SWEDAC) which issued the standard.
In 1991, researchers at the National Institute for Occupational Safety and Health (NIOSH) studied two groups of telephone operators. One group used VDT displays; the other did not. The levels of power-frequency magnetic fields (60 Hz) measured at the operators' locations were similar for the two groups. This study reported that miscarriages happened no more often among full-time VDT users than among those workers not using VDTs. The study also reported that there appeared to be no relationship between the amount of time a woman used a VDT and her chance of having a miscarriage.
A study from Finland (Lindbohm et al., 1992) reported that women who miscarried at one of three companies were more likely to have used models of VDTs that could produce 50-Hz magnetic fields above 3 mG. Finnish investigators did not find an overall link between miscarriage or birth defects and VDT use, nor was there a relationship between increased incidence of miscarriages with increasing VLF field strength.
Recently, a large study at Yale focused on the effects of EMF exposure on the growth rate of the unborn child (Bracken et al., 1995). These researchers obtained information about power frequency magnetic field exposure from power line and home sources. VDT use over 20 hours a week was not found to affect the weight or growth rate of the baby, nor did the mother's exposure to higher magnetic fields or to "high" field sources such as electrically heated beds.
In 1994, the National Radiological Protection Board (NRPB) of Great Britain invited an advisory group of scientists to review studies of possible health effects related to the use of VDTs. They concluded that there was "no good reason to suppose" that exposure to low frequency electromagnetic fields from the use of VDTs harms the unborn child.