Epidemiological study (observational study)

Maternal exposure to magnetic fields during pregnancy in relation to the risk of asthma in offspring epidem.

By: Li DK, Chen H, Odouli R

Published in: Arch Pediatr Adolesc Med 2011; 165 (10): 945-950

Aim of study (acc. to author)

A prospective cohort study was conducted in the USA to investigate the relationship between maternal exposure to magnetic fields during pregnancy and the risk of asthma in offspring.

Further details

The present study is based on the prospective cohort study that was conducted to examine the effect of exposure to electromagnetic fields on the risk of miscarriage among pregnant members of Kaiser Permanente Northern California who were recruited from 1996 to 1998 (Li et al (2002)). After birth the children were followed up until the age of 13 for the diagnosis of asthma. To be considered as a case of asthma, a child had to have received a clinical diagnosis of asthma on at least 2 occasions within a 1-year period during follow-up.

Endpoint/type of risk estimation

asthma

Type of risk estimation:

incidence

(hazard ratio)

Exposure

- 50/60 Hz
- magnetic field
- power transmission line
- other domestic appliance
- residential
- personal

Assessment

measurement: 24 h-measurements of the magnetic fields in the frequency range of 40 to 800 Hz every 10 seconds

Exposure groups

Group	Description
Reference group 1	maternal exposure to magnetic fields, 24 h-measurement: low, ≤ 0.03 µT
Group 2	maternal exposure to magnetic fields, 24 h-measurement: medium, > 0.03 - 0.2 µT
Group 3	maternal exposure to magnetic fields, 24 h-measurement: high, > 0.2 µT

Population

Group:
- children
- children in utero
Age: 0–13 years
Characteristics: children whose mothers were pregnant between 1996 - 1998
Observation period: 1996 - August 2010
Study location: USA (San Francisco area)
Data source: cohort of Kaiser Permanente Northern California, USA
Exclusion criteria: insufficient English language skills

Study size

Type	Value
Total	829
Evaluable	626

Statistical analysis method:

Cox proportional regressions analysis

(adjustment:

maternal age, ethnicity, education, smoking during pregnancy, and history of asthma

)

Results (acc. to author)

A statistically significant linear dose-response relationship was found between increasing maternal median daily magnetic field exposure level in pregnancy and an increased risk of asthma in offspring. Every 0.1 µT increase of maternal magnet field level during pregnancy was associated with a 15 % increased rate of asthma in offspring (adjusted hazard ratio: 1.15; CI 1.04- 1.27). Using the categorical magnetic field level, the results showed a similar dose-response relationship: compared with the children whose mothers had a low magnetic field level (< 0.03 µT) during pregnancy, children whose mothers had a high magnetic field level (> 0.2 µT) had more than a 3.5-fold increased rate of asthma, while children whose mothers had a medium magnetic level (> 0.03-0.2 µT) had a 74% increased rate of asthma. A statistically significant synergistic interaction was observed between the magnetic field effect and a maternal history of asthma and birth order (firstborn).
The authors conclude that their findings provide new epidemiological evidence that high maternal magnetic field levels in pregnancy may increase the risk of asthma in offspring.

Limitations (acc. to author)

Exposure to magnetic fields was measured on only once for 24 hours.

Study funded by

California Public Health Foundation, USA

Comments on this article

Brain JD et al. (2012): Observations on power-line magnetic fields associated with asthma in children
Villeneuve PJ (2012): Exposure to magnetic fields during pregnancy and asthma in offspring
Li DK et al. (2012): Author's reply: Observations on Power-Line Magnetic Fields Associated With Asthma in Children
Yost MG et al. (2011): A recurring question: are there health effects of power-frequency magnetic fields?

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