Previous studies have reported associations between prenatal cell phone use (exposure to radiofrequent fields) and child behavioral problems. In this study data from 83,884 mother-child pairs in the five cohorts from Denmark (1996-2002), Korea (2006-2011), the Netherlands (2003-2004), Norway (2004-2008), and Spain (2003-2008) were analyzed. Cell phone use was grouped into none, low, medium, and high, based on frequency of calls during pregnancy reported by the mothers. Evidence for a trend of increasing risk of child behavioral problems through the maternal cell phone use categories was observed for hyperactivity/inattention problems; ADHD (OR for problems in the clinical range: 1.11, 95%CI 1.01, 1.22; 1.28, 95%CI 1.12, 1.48, among children of medium and high users, respectively). Thus, maternal cell phone use during pregnancy may be associated with an increased risk for behavioral problems, particularly hyperactivity/inattention problems, in the offspring. Increased risk was also found in the high cell phone use category for overall behavioral problems and emotional problems, although not statistically significant. The study can be found here.
In all analyses low cell phone use was used as the reference category. For no cell phone use decreased risk was found for all studied behavioral problems (overall problems, ADHD and emotional problems). It is unclear why low cell phone use instead of no cell phone use was used as the reference category. Using subjects that never used a cell phone would have given higher risk estimates in the high use category.
In the Dutch cohort cordless phone use was assessed yielding similar results as for cell phone use.