Reproductive outcomes and disorders

Conclusions of the expert review bodies

View of ICNIRP

A major review of epidemiology by ICNIRP published in 2001 concluded:

(note: this paper was written before two recent results from California which are discussed by the NRPB - see below)

"Thus fundamental methodological limitations preclude firm conclusions about reproductive outcomes. Studies with refined measurements of exposure and outcome could yield different results than those reported to date. However, on the basis of theoretical considerations and both experimental and epidemiological studies, there is very little encouragement for pursuing research on EMF and reproductive health. Existing evidence does not support the hypothesis that maternal exposure to EMF through residential, including heated bed, exposure or through the workplace is associated with adverse pregnancy outcomes." More on ICNIRP

View of NRPB

A statement by the NRPB’s Advisory Group on “Magnetic fields and miscarriage”, April 2002 discusses two recent papers on magnetic fields and miscarriage from California. It concludes:

"Conclusion
Neither study provides substantial evidence of increased risk of miscarriage attributable to exposure to above average magnetic fields and neither justifies regulatory action. It would be expensive and difficult to carry out further epidemiological investigation that would address the issue robustly and, in the absence of a plausible biological mechanism that would link such exposure to miscarriage, it is arguable whether it would be justifiable to support research of this type. If further study is required, it would be worth financing only if a large cohort of (say) 2000 women could both be interviewed and have measurements made of their exposures over a period of at least 24 hours less than 8 weeks after their last menstrual period and have repeat measurements made on at least two further occasions within the next 8 weeks to determine the consistency of the exposures throughout early pregnancy and their temporal relationship to miscarriage." More on NRPB

In its new advice on exposure guidelines in 2004, the NRPB stated:

“The overall evidence from studies of maternal exposure to ELF EMFs in the workplace does not indicate an association with adverse pregnancy outcomes, while studies of maternal exposure in the home are difficult to interpret.” More on NRPB

View of WHO

The WHO Environmental Health Criteria Monograph published in 2007 concluded:

"On the whole,epidemiological studies have not shown an association between adverse human reproductive outcomes and maternal or paternal exposure to ELF fields. There is some evidence for an increased risk of miscarriage associated with maternal magnetic field exposure, but this evidence is inadequate.

Overall, the evidence for developmental and reproductive effects is inadequate."

More on the WHO Monograph

One recent study of stillbirth

At the top of this page, we summarise the conclusions of expert review bodies on magnetic fields and reproductive outcomes.  But those reviews are now several years old.  We give here the abstract from a recent study of stillbirth and residential proximity to power lines.

Occup Environ Med. 2011 Jul 8. [Epub ahead of print]
Stillbirth and residential proximity to extremely low frequency power transmission lines: a retrospective cohort study.
Auger N, Park AL, Yacouba S, Goneau M, Zayed J.
SourceInstitut national de santé publique du Québec, Montréal, Québec, Canada. 

 Abstract
Objectives The relationship between electromagnetic field exposure and stillbirth has not been evaluated. We assessed associations between residential proximity to extremely low frequency power transmission lines and stillbirth across gestational age. Methods Data included singleton live births (N=514 826) and stillbirths (N=2033) for 1998-2007 in metropolitan areas of Québec, Canada. Using power transmission line maps, the distances between lines and residential six-digit postal codes (<25, 25-49.9, 50-74.9, 75-99.9, ≥100 m) were calculated. Generalised estimating equations were used to compute ORs and 95% CIs for distance and stillbirth, accounting for individual and area characteristics. Early preterm (<28 weeks), late preterm (28-36 weeks) and term (≥37 weeks) stillbirths were examined relative to fetuses-at-risk. Results There was no association between distance and preterm stillbirth. The odds of term stillbirth for <25 m were greater compared to ≥100 m (OR 2.25, 95% CI 1.14 to 4.45), but no dose-response pattern was apparent. Conclusions A graded dose-response trend between distance to lines and odds of stillbirth was not found, but the likelihood of term stillbirth was elevated for residences within 25 m of power transmission lines. Residential proximity to transmission lines is unlikely to be associated with stillbirth, but more research is needed to rule out a possible link.

Birth weight

Two recent UK studies have suggested that proximity to power lines may be associated with low birth weight.  The first found a fairly strong effect.  the second, on the same subjects but using improved analytical techniques, still found an effect but a rather smaller one.

SCENIHR (the EU's scientific committee) considered these two studies in their 2015 Opinion and made various criticisms of the methodology, concluding:

In conclusion, recent results do not show an effect of the ELF fields on the reproductive function in humans.

Abstracts

Bioelectromagnetics. 2014 Apr;35(3):201-9.
Maternal residential proximity to sources of extremely low frequency electromagnetic fields and adverse birth outcomes in a UK cohort.
de Vocht F, Hannam K, Baker P, Agius R. 

 

Studies have suggested that exposure to extremely low frequency electromagnetic fields (ELF-EMF) may be associated with increased risk of adverse birth outcomes. This study tested the hypothesis that close proximity to residential ELF-EMF sources is associated with a reduction in birth weight and increased the risk of low birthweight (LBW), small for gestational age (SGA) and spontaneous preterm birth (SPTB). Closest residential proximity to high voltage cables, overhead power lines, substations or towers during pregnancy was calculated for 140356 singleton live births between 2004 and 2008 in Northwest England. Associations between proximity and risk for LBW, SGA and SPTB were calculated, as well as associations with birth weight directly. Associations were adjusted for maternal age, ethnicity, parity and for part of the population additionally for maternal smoking during pregnancy. Reduced average birth weight of 212 g (95% confidence interval (CI): -395 to -29 g) was found for close proximity to a source, and was largest for female births (-251 g (95% CI: -487 to -15 g)). No statistically significant increased risks for any clinical birth outcomes with residential proximity of 50 m or less were observed. Living close (50 m or less) to a residential ELF-EMF source during pregnancy is associated with suboptimal growth in utero, with stronger effects in female than in males. However, only a few pregnant women live this close to high voltage cables, overhead power lines, substations or towers, likely limiting its public health impact.

 

Environ Int. 2014 Aug;69:51-7.
Residential proximity to electromagnetic field sources and birth weight: Minimizing residual confounding using multiple imputation and propensity score matching.
de Vocht F, Lee B. 

 

Studies have suggested that residential exposure to extremely low frequency (50 Hz) electromagnetic fields (ELF-EMF) from high voltage cables, overhead power lines, electricity substations or towers are associated with reduced birth weight and may be associated with adverse birth outcomes or even miscarriages. We previously conducted a study of 140,356 singleton live births between 2004 and 2008 in Northwest England, which suggested that close residential proximity (≤ 50 m) to ELF-EMF sources was associated with reduced average birth weight of 212 g (95%CI: -395 to -29 g) but not with statistically significant increased risks for other adverse perinatal outcomes. However, the cohort was limited by missing data for most potentially confounding variables including maternal smoking during pregnancy, which was only available for a small subgroup, while also residual confounding could not be excluded. This study, using the same cohort, was conducted to minimize the effects of these problems using multiple imputation to address missing data and propensity score matching to minimize residual confounding. Missing data were imputed using multiple imputation using chained equations to generate five datasets. For each dataset 115 exposed women (residing ≤ 50 m from a residential ELF-EMF source) were propensity score matched to 1150 unexposed women. After doubly robust confounder adjustment, close proximity to a residential ELF-EMF source remained associated with a reduction in birth weight of -116 g (95% confidence interval: -224:-7 g). No effect was found for proximity ≤ 100 m compared to women living further away. These results indicate that although the effect size was about half of the effect previously reported, close maternal residential proximity to sources of ELF-EMF remained associated with suboptimal fetal growth.