De-Kun
Li, MD, PhD; Hong Chen, MPH; Roxana Odouli, MSPH
�
Arch
Pediatr Adolesc Med. Published online August 1,
2011. doi:10.1001/archpediatrics.2011.135
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Objective�
To determine whether maternal exposure to high
levels of magnetic fields (MFs) during pregnancy
is associated with the risk of asthma in
offspring.
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Design�
A prospective cohort study.
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Setting�
Kaiser Permanente Northern California.
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Participants�
Pregnant Kaiser Permanente Northern California
members in the San Francisco area.
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Main
Outcome Measures� Asthma was clinically diagnosed
among 626 children who were followed up for as
long as 13 years. All participants carried a meter
to measure their MF levels during pregnancy.
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Results�
After adjustment for potential confounders, a
statistically significant linear dose-response
relationship was observed between increasing
maternal median daily MF exposure level in
pregnancy and an increased risk of asthma in
offspring: every 1-mG increase of maternal MF
level during pregnancy was associated with a 15%
increased rate of asthma in offspring (adjusted
hazard ratio [aHR], 1.15; 95% confidence interval
[CI], 1.04-1.27). Using the categorical MF level,
the results showed a similar dose-response
relationship: compared with the children whose
mothers had a low MF level (median 24-hour MF
level, 0.3 mG) during pregnancy, children whose
mothers had a high MF level (>2.0 mG) had more
than a 3.5-fold increased rate of asthma (aHR,
3.52; 95% CI, 1.68-7.35), while children whose
mothers had a medium MF level (>0.3-2.0 mG) had
a 74% increased rate of asthma (aHR, 1.74; 95% CI,
0.93-3.25). A statistically significant
synergistic interaction was observed between the
MF effect and a maternal history of asthma and
birth order (firstborn).
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Conclusion�
Our findings provide new epidemiological evidence
that high maternal MF levels in pregnancy may
increase the risk of asthma in offspring.
Author Affiliations: Division of Research, Kaiser
Foundation Research Institute, Kaiser Permanente,
Oakland, California.