Maternal exposure to extremely low frequency magnetic fields: Association with time to pregnancy and foetal growth.

Background: Data on reproductive and developmental effects of extremely low frequency magnetic fields (ELF MFs) are inconclusive. This study tested the hypothesis that maternal exposure to ELF MFs is associated with increased time to pregnancy (TTP), reduced birthweight or small for gestational age (SGA).

Methods: The study cohort consisted of 373 mothers who gave birth between 1990 and 1994 in Kuopio University Hospital, Finland. To increase prevalence of high ELF MF exposure, women living in buildings near known ELF MF sources were included. Maternal exposure to ELF MF before and during pregnancy was assessed with short term measurements in residences and questionnaires. Associations between ELF MF exposure and TTP, low birth weight and SGA were analysed by logistic regression (or linear regression for continuous variables), adjusting for factors known to be associated with the selected pregnancy outcomes, such as maternal smoking, alcohol consumption and socioeconomic status.

Results: The MF exposure of the mothers was slightly higher than in Finnish residences in general, but very high exposures (>0.4μT) were rare. No consistent association of ELF MF with TTP, birth weight or SGA was found.

Conclusions: ELF MF exposure is not likely to be associated with TTP or prenatal growth at residential exposure levels that were observable in this study.