What does the science suggest?
The exposure limits for EMFs are designed to protect against the established effects of EMFs on the body, whereby EMFs induce currents and voltages that can interfere with nerves. There is no established mechanism whereby either a pregnant woman or the baby she is carrying would be any more sensitive to these effects than any other adult. The evidence on exposure to magnetic magnetic fields and pregnancy outcomes is broadly reassuring - see a summary of what the review bodies have said.
It is, of course, possible to speculate that the developing foetus may be more sensitive to these or other effects, but this is speculation. On the other hand, there may be an entirely understandable wish to take an extra level of precaution when it comes to pregnancy.
What do the exposure limits say?
Many of the EMF exposure guidelines that have been published make no specific reference to pregnant women. The issue is not mentioned explicitly in ICNIRP 1998, EU 1999, or ICES 2002.
NRPB 2004 does mention pregnant women but only specifically in the context of radiofrequency (RF) EMFs. For RF EMFs they suggest that the foetus may be more susceptible to heating effects than the adult is, so the public exposure limits (which are lower than the occupational limits) should apply to all pregnant women, to ensure excess heating does not occur. Power-frequency EMFs do not cause heating, so this argument does not directly apply to power-frequency EMFs.
ICNIRP 2010 does not specifically say anything about pregnant women in its actual recommended guidelines. But in the "definitions" it does say:
"General public
The term General public refers to the entire population. It includes individuals of all ages, and of varying health status, and this will include particularly vulnerable groups or individuals such as the frail, elderly, pregnant workers, babies and young children."
This implies that pregnant women may be regarded as "particularly vulnerable". But it doesn't specifically say how to treat pregnant women who are at work.
The 2011 Commission draft of the Directive on occupational exposures says:
"Where a worker has declared to her employer that she is pregnant then the requirements of Council Directive 92/85/EEC on the introduction of measures to encourage improvements in the safety and health at work of pregnant workers and workers who have recently given birth or are breastfeeding apply. The employer shall enable the worker to avoid having to enter areas where exposures exceeding the exposure limits for the general public given in Council Recommendation 1999/519/EC, or its subsequent revisions."
What would be a sensible approach?
The various exposure guidelines all agree that there is no need for exposure limits for pregnant women any more restrictive than the limits that apply to all members of the public. The public exposure limits are valid for pregnant women and their unborn babies.
When a pregnant woman is at work, the wording of the various existing exposure guidelines implies it is acceptable to continue to use the occupational guidelines, which are higher than the public guidelines. But as a precautionary measure, it may be sensible to apply the public guidelines to pregnant women at work. If the present Commission draft of the EU Directive comes into force, this would become a requirement.
This is the approach taken by National Grid.
