The risk of miscarriage and birth defects among women who use visual display terminals during pregnancy.

Use of visual display terminals (VDTs) was examined in a case-control study of pregnancy outcome among 1,583 pregnant women who attended three Kaiser Permanente obstetrics and gynecology clinics in Northern California, 1981-1982. We found a significantly elevated risk of miscarriage for working women who reported using VDTs for more than 20 hr per week during the first trimester of pregnancy compared to other working women who reported not using VDTs (odds ratio 1.8, 95% CI: 1.2-2.8). This risk could not be explained by age, education, occupation, smoking, alcohol consumption, or other maternal characteristics. No significantly elevated risk for birth defects was found among working women although odds ratios were 1.4 for both moderate and high VDT exposure, compared with no exposure (95% CI: 0.7-2.7 and 0.7-2.9, respectively). One possible explanation for these findings is that women who had adverse pregnancy outcomes may have overreported their exposures to VDTs and/or women with normal births may have underreported theirs. The findings may also be due to unmeasured factors confounded with high VDT use such as poor ergonomic conditions or job-related stress. That VDTs themselves are hazardous to the pregnant operator remains a possibility. Our results underscore the need for large cohort studies of working women that will provide objective measures of VDT exposures, ergonomic factors, and stress.