Li et al1 report an association between childhood asthma and maternal magnetic field exposure of 2 mG or more during pregnancy, based on a single day of personal magnetic field (40-800 Hz) measurement. While we have a common interest in understanding the causes and prevention of asthma, we offer the following concerns.
Correspondence: Dr Valberg, Gradient, 20 University Rd, Cambridge, MA 02138 (email@example.com).
Author Contributions:Study concept and design: Brain, Kavet, and Valberg. Analysis and interpretation of data: Brain and Kavet. Drafting of the manuscript: Brain, Kavet, and Valberg. Critical revision of the manuscript for important intellectual content: Brain and Kavet. Statistical analysis: Valberg. Administrative, technical, and material support: Brain and Kavet. Study supervision: Brain.
Financial Disclosure: None reported.