Physical activity and magnetic field exposure in pregnancy

Background: Peak magnetic field exposure was associated with increased risk of miscarriage in 2 recent studies. Reduced physical activity levels in healthy pregnancies may affect measured exposure and thus bias results. Methods: We recruited 100 pregnant women to wear an Actigraph accelerometer and EMDEX magnetic field monitor for a 7-day period. We evaluated the association between physical activity and magnetic field exposure (peaks and time-weighted average) using generalized estimating equations and linear mixed models. Results: We found a positive association between level of activity and likelihood of incurring elevated exposure in the person-day analysis, most strongly for cutpoints of 16 or 20 mG, for both working and nonworking women among whom odds ratios in the uppermost quartile ranged from 2.1 to 2.6. A positive association was found using person-minutes only among nonworking women. Conclusion: Physical activity may affect peak magnetic field exposure. If the early nausea and later cumbersomeness of healthy pregnancies leads to reduced physical activity, this could distort measured magnetic field‐health outcome associations.