Worker Health Study Summaries
Research on long-term exposure
Video Display Terminal Operators (Electromagnetic Fields)
NIOSH researchers completed a study of the effects of Video Display Terminal (VDT) use during pregnancy. In 1987 and 1988, we interviewed women using VDT’s about reproductive health, including any pregnancies. The study found no increased risk of reduced birth weight (RBW) or preterm babies.
Why and How We Did Our Study
We did this study because we were concerned that VDT use during pregnancy caused miscarriages or other pregnancy problems. Previously, we found that VDT operators did not have an increased risk of miscarriages compared to non VDT users. Then we asked if operators who worked with VDTs during pregnancy had a greater risk of having reduced birth weight babies or preterm births. We also wanted to know if VDT users had a higher risk of having babies with birth defects or babies who died within 7 days of birth.
We studied two groups of women. One group was directory assistance operators who used VDTs during pregnancy. The other group was general long distance operators who did not use VDTs during pregnancy.
Both VDT and general operators were exposed to a low amount of electromagnetic fields (EMFs). The VDT users had slightly higher levels of EMFs than the general operators.
From interviews and birth certificates, NIOSH researchers obtained information on preterm births, birth weights, birth defects, and early deaths. Information on VDT use at work during pregnancy was obtained from company records.
Both VDT users and general operators had very few babies that meet the medical definition of low birth weight (LBW) which is 5.5 pounds (lbs.) or less. Only 3.6% of VDT users and 4.3% of general operators had babies who weighed 5.5 lbs or less. Both of these percentages were much less than the U.S. rate of 7.1% for low birthweight babies. To do our study effectively, we defined a “Reduced Birth Weight” (RBW) baby as one who weighed less than 6.2 pounds at birth.
- We found that women who had worked with VDTs during pregnancy did not have an increased risk of having RBW or preterm babies. Women who worked with VDTs during pregnancy had 8.9% RBW babies compared to 9.7% for general operators. VDT users had slightly fewer preterm births (7.9%) than general operators (11.2%). We considered a baby preterm if the baby was born between 21-37 weeks of pregnancy.
- We found major birth defect rates of 2.3% in VDT users and 1% in the general operators. These rates are similar to the 2-3% rate for major birth defects in infants of U.S. women.
- The rate of early infant deaths was 1.0% in the VDT users and 0.5% in the general operators. The numbers of birth defects and early infant deaths were too small to study in detail.
Our study also found these risk factors for certain women, both for VDT users and non-VDT users:
- Women who smoked more than 10 cigarettes per day were more likely to have an RBW baby than non-smoking women.
- Women who had high blood pressure during pregnancy had more RBW babies.
- Women who had certain complications (toxemia or preeclampsia) during their pregnancy were more likely to have preterm babies. This was expected, because doctors may have to induce labor early in women who have these conditions.
- Women diagnosed with diabetes during or before their pregnancy also were more likely to have a preterm baby.
In summary, VDT use during pregnancy did not increase a woman’s risk of having a preterm birth or a reduced birth weight baby.
For more information please call the NIOSH toll-free number at 800-356-4674
Schnorr T (1990). The NIOSH study of reproductive outcomes among video display terminal operators. Reproductive Toxicology 4: 61-65. (Study Report).
Schnorr T, Grajewski B, Hornung R et al (1991). Video display terminals and the risk of spontaneous abortions. The New England Journal of Medicine 324 (11): 727-733.
Grajewski B, Schnorr T, Reefhuis J et al. (1997). Work with video display terminals and the risk of reduced birthweight and preterm birth. American Journal of Industrial Medicine 32:681-688.