Asthma cases were identified using 3 independent data sources: mothers' reports, a national hospitalization registry and a national prescription drug registry. A definitive asthma case was a child who had an asthma diagnosis in all of the three data sources.
|Reference group 1||magnetic field strength: no exposure|
|Group 2||magnetic field strength: 0.1 µT|
|Group 3||magnetic field strength: ≥ 0.2 µT|
Among possible asthma cases, only 24 (0.12%) had mothers who were exposed to magnetic field strength of 0.2 µT or more during pregnancy and only 38 (0.19%) were exposed at any time during follow-up.
No differences or trends in the risk of asthma development were detected between children with different levels of MF exposure regardless of the asthma case definition or outcome data source.
The authors concluded that no evidence was found for an association between residential exposure to magnetic fields during pregnancy or early childhood and the risk of childhood asthma.