Maternal Exposure to Magnetic Fields During Pregnancy in Relation to the Risk of Asthma in Offspring
De-Kun Li, MD, PhD; Hong Chen, MPH; Roxana Odouli, MSPH
Objective: To determine whether maternal exposure to
high levels of magnetic fields (MFs) during pregnancy
is associated with the risk of asthma in offspring.
Design: A prospective cohort study.
Setting: Kaiser Permanente Northern California.
Participants: Pregnant Kaiser Permanente Northern
California members in the San Francisco area.
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.
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 highMFlevel (-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).
Conclusion: Our findings provide new epidemiological
evidence that high maternal MF levels in pregnancy
may increase the risk of asthma in offspring.
Arch Pediatr Adolesc Med.
Published online August 1, 2011.
doi:10.1001/archpediatrics.2011.135
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