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.


CONCLUSIONS
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.
Savitz
David A
DA
Department of Epidemiology School of Public Health, and Carolina Population Center, University of North Carolina, Chapel Hill, USA. david_savitz@unc.edu
Herring
Amy H
AH
Mezei
Gabor
G
Evenson
Kelly R
KR
Terry
James W
JW
Kavet
Robert
R
D000328:Adult; D015982:Bias; D004574:Electromagnetic Fields; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D018670:Monitoring, Ambulatory / Q000295:instrumentation; D009043:Motor Activity; D009657:North Carolina; D011247:Pregnancy; D012307:Risk Factors