Maternal cell phone use during pregnancy and child cognition at age 5 years in 3 birth cohorts
Introduction
There has been widespread growth in the use of cell phones in recent decades, with an estimated 7.7 billion cell phone subscribers at the end of 2017 worldwide (International Telecommunication Union, 2018). Despite the popularity and usefulness of this technology, there remain questions about its safety, including concern about the potential, but as-of-yet unconfirmed, health effects of radiofrequency (RF) fields emitted from cell phones. If RF exposure from cell phones is harmful to health, fetuses and children may be at increased risk due to their rapidly developing tissue systems (Kheifets et al., 2005; Wiart et al., 2008).
Studies in rodents have reported some links between extended exposure to RF-EMF in pregnant dams and hyperactivity, altered neurological development, oxidative stress, and impaired cognition in offspring (Haghani et al., 2013; Aldad et al., 2012; Zhang et al., 2015; Ozgur et al., 2013), while another study did not support these findings (Shirai et al., 2014). However, RF exposure modeling studies have demonstrated that a cell phone held close to the body by a pregnant woman would result in a very low specific absorption rate (SAR) of RF in the fetus (Cabot et al., 2014), which is unlikely to have biological effects (Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR), 2015; Consales et al., 2012; Kovacic and Somanathan, 2010), but exposure levels could vary depending on the position of the phone and fetus (Varsier et al., 2014). An experimental study performed among pregnant volunteers reported changes in the protein profile of chorionic tissue in early pregnancy in relation to RF exposure from cell phones held close to the abdomen (Luo et al., 2013). Although experimental and modeling studies have provided some evidence for potential biological effects of RF-EMF, the relevance of these findings to human health is unclear, and in-utero RF-EMF exposure from a phone held close to the head would be much lower than exposure from a phone held close to the abdomen. A biological mechanism to explain the potential health effects of cell phones has not been identified, but several mechanisms have been proposed, including induction of oxidative stress, activation of heat shock proteins which increase the permeability of the blood brain barrier, and calcium ion leakage in neuronal tissues (Consales et al., 2012; Kovacic and Somanathan, 2010; Irmak et al., 2002; Altunkaynak et al., 2016).
Several investigations in the Danish National Birth Cohort (DNBC) have consistently found associations between maternal cell phone use during pregnancy and emotional and behavioral difficulties in children at ages 7 and 11 years of age. The strongest association was seen among children exposed both prenatally (mother used a cell phone while pregnant) and postnatally (child used a cell phone at age 7 years), with an odds ratio (OR) of 1.80 and a 95% confidence interval (CI) of 1.45 to 2.23 when compared to those with no exposure (Divan et al., 2008). These findings were replicated in a separate group of DNBC children who were born later, and with the two samples combined. Adjustment for numerous additional potential confounders weakened but did not eliminate the associations (Divan et al., 2012). A more recent prospective study from the DNBC found similar associations between prenatal cell phone exposures and cell phone use at age 7 years and behavioral problems in children at age 11 years (Sudan et al., 2016a). In the Amsterdam Born Children and their Development (ABCD) cohort from The Netherlands, investigators did not find associations between prenatal cell phone use and behavioral problems in children at age 5 years (Guxens et al., 2013), but their results were not inconsistent with the findings in the DNBC as the CI's overlapped (Sudan et al., 2013). A recent analysis of individual participant data from 5 cohort studies, which included the DNBC and ABCD, reported increased odds of hyperactivity/inattention in 5–7 year-old children of mothers who were frequent cell phone users during pregnancy (Birks et al., 2017).
A few birth cohort studies have also examined associations between maternal prenatal cell phone use and early childhood development and cognition. Studies in the DNBC (Divan et al., 2011) and the Spanish Environment and Childhood Project (INMA) (Vrijheid et al., 2010) did not find associations between prenatal cell phone use and developmental or cognitive delays in early childhood at 6, 14, and 18 months of age. A study from the Norwegian Mother and Child Cohort (MoBa) (Papadopoulou et al., 2017) found decreased odds of low language and motor skills at age 3 years and no evidence of adverse neurodevelopmental effects in relation to prenatal maternal cell phone use. An investigation in the Korean Mothers and Children's Environmental Health Study (MOCEH) (Choi et al., 2017) reported no association between prenatal RF exposure and child neurodevelopment up to age 3 years, but did find a potential combined effect of prenatal exposure to lead and maternal prenatal cell phone use on neurodevelopment.
To date, few epidemiologic studies relating prenatal cell phone exposure to childhood cognition have been conducted. Given the widespread use of cell phones, further scrutiny of this relationship is warranted. Therefore, we investigated the association between cell phone use by women during pregnancy and cognition scores in their children in three birth cohorts.
Section snippets
Methods
This investigation is part of the Generalized EMF Research using Novel Methods (GERoNiMO) Project (GERoNiMO, 2014), and included data from 3 population-based prospective birth cohorts from Europe and Asia: the DNBC (Olsen et al., 2001), INMA (Guxens et al., 2012), and MOCEH (Kim et al., 2009) (Table 1). Enrollment in the three cohorts spanned 1996–2010 (Table 1). Across all 3 cohorts, data on both cell phone use during pregnancy and child cognition were available for 3089 mother-child pairs,
Results
On average, mothers in this study were 31 years old at the time of their child's birth, with little variation between cohorts (Table 3). About half of the children in the study were their mother's first child, but a greater number of Danish mothers had given birth to two or more children previously (16.1%) than in other cohorts. More Spanish mothers reported a history of psychiatric problems (17.6%), and fewer Spanish mothers and fathers completed university or higher levels of education
Discussion
We observed a general pattern of lower cognition scores in relation to high frequency of use compared to low frequency use across all cognitive dimensions, but the findings were imprecise. Tests for heterogeneity across cohorts and the proportion of variation in the standardized mean differences across cohorts indicated that results were generally similar in all cohorts.
Previous studies in individual birth cohorts did not report associations between maternal prenatal cell phone use/RF exposure
Funding
The authors would like to thank the mothers and children that participated in the cohort studies.
GERoNiMO project: This work is supported by the European Union (grant 603794).
DNBC: This work was supported by the Danish Epidemiology Science Centre; The Lundbeck Foundation (grant 195/04); Egmont Foundation; March of Dimes Birth Defect Foundation; Agustinus Foundation; and the Medical Research Council (grant SSVF 0646); The largest source of funds was provided by the Centers for Disease Control in
Conflict of interest
The authors have no conflicts of interest to declare.
Declarations of interest
None.
Acknowledgements
The authors would like to thank the study data managers for each cohort, and the mothers and children for their time and participation.
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