Miscarriage rates could nearly double if Transpower's electricity line through the Waikato goes ahead in its planned form, according to a scientific study.

A United States study showing an 80 per cent likelihood of increased miscarriages was presented by video link at a health forum organised by power line opponents at the University of Waikato at the weekend.

Excessive exposure to electromagnetic fields (EMF) has also been linked to childhood leukaemia, brain cancer, Lou Gehrigs motor neuron disease, and depression.

De-Kun Li, of Oakland's Kaiser Foundation Research Institute, studied 969 pregnant women in San Francisco about three years ago and found they had an 80 per cent greater chance of miscarriage if exposed to more than 1.6 microteslas of magnetic forces.

That level of exposure would occur about 50 metres away from the 400kV transmission line proposed by Transpower.

Transpower's proposed 65-metre wide easement for the Whakamaru-Otahuhu transmission line would see landowners getting exposure of 7-8 microteslas.

At the forum, attended by about 100 people, New Era Energy (NEE), a lobby group opposing the power line, launched a proposed new standard for EMF of 0.1 microteslas, a thousand times less than the current New Zealand standard of 100 microteslas.

New Era Energy vice-chairman Bob McQueen said if the Electricity Commissioner agreed to adopt the new standard, it would force Transpower to buy 600 metres of land for easements compared to the present 65 metres.

Power line opponents believe the extra land compensation costs would make Transpower's plan uneconomic.

New Zealand's 100 microtesla maximum exposure limit is based on recommendations from the Health Ministry's National Radiation Laboratory.

Transpower has said it will stick with its 65-metre easements.

Also at the forum, Californian doctor Raymond Neutra summarised the results of an evaluation he and other scientists had done as part of a $7 million study on behalf of the Californian Department of Health Services (DHS).

"To one degree or another, all three of the DHS scientists are inclined to believe that EMFs can cause some degree of increased risk of childhood leukaemia, adult brain cancer, Lou Gehrigs disease and miscarriage," he said.

South Auckland surgeon Robin Smart, whose Clevedon property is affected by the power line plan, said he believed the health concerns related to EMF were now proven.

"Since 1979 there's been a huge number of well-conducted studies which have statistically proven arguments about the health risks."

Mr Smart said New Zealand's current maximum exposure level was completely arbitrary. He said no one could actually live with an exposure of 100 microteslas as it would be about 30cm away from a transmission line.

"If people are going to have these lines inflicted upon them, then given the weight of scientific studies, they should be no closer than 0.1 microtesla exposure which in this case means a 600-metre easement."

- nzpa