Maternal cumulative exposure to extremely low frequency electromagnetic fields and pregnancy outcomes in the Elfe cohort

Objectives: To study the relations between maternal cumulative exposure to extremely low frequency electromagnetic fields (ELF EMF) and the risk of moderate prematurity and small for gestational age within the Elfe cohort. Methods: The Elfe study included 18,329 infants born at 33 weeks of gestation or more in France in 2011 and was designed to follow the children until 20 years of age. Gestational age and anthropometric data at birth were collected in medical records and small for gestational age was defined according to a French customized growth standard. During interviews, mothers were asked to report their job status during pregnancy. If employed, their occupation was coded according to the International Standard Classification of Occupations 1988 and the date on which they stopped their work was recorded. Cumulative exposure to ELF EMF during pregnancy was assessed, for both mothers who worked and those who did not during pregnancy, using a recently-updated job-exposure matrix (JEM). Cumulative exposure was considered as a categorical variable (< 17.5, 17.5-23.8, 23.8-36.2, 36.2-61.6 or >= 61.6 mu T-days), a binary variable (< 44.1 and >= 44.1 mu T-days) and a continuous variable. Associations were analyzed by logistic regression, adjusting for the mother's lifestyle factors, socio-demographic characteristics and some mother's medical history during and before pregnancy. Analyses were restricted to single births and to complete values for the pregnancy outcomes (n = 16,733). Results: Cumulative exposure was obtained for 96.0% of the mothers. Among them, 37.5% were classified in the 23.8-36.2 mu T-days category, but high exposures were rare: 1.3% in the >= 61.6 mu T-days category and 5.5% in the >= 44.1 mu T-days category. No significant association was observed between maternal cumulative exposure and moderate prematurity and small for gestational age in this exposure range. Conclusion: This large population-based study does not suggest that maternal exposure to ELF EMF during pregnancy is highly associated with risks of moderate prematurity or small for gestational age.