By Robert Uhlig, Technology Correspondent

New research has raised doubts over the safety of ultrasound scans used to view fetuses in the womb. Scientists have called for further research to determine whether safety limits should be reviewed for the tests, which are also used to check internal organs in children and adults. Since the early 1990s, when American researchers showed that ultrasound tissue heating can cause bleeding in mouse intestines, ultrasonographers tune the power of scans to reduce heating. The latest discovery, by scientists at University College Dublin, is the first to find that scans create changes in cells. Patrick Brennan, who led the research, said: "It has been assumed for a long time that ultrasound has no effect on cells. We now have grounds to question that assumption."

The researchers gave 12 mice an eight megahertz scan lasting for 15 minutes. Hospital scans can last for up to an hour, using frequencies of between three and 10 megahertz. According to today's New Scientist, two significant changes in the cells of the small intestine were detected in scanned mice compared with unscanned mice. Four and a half hours after exposure, the rate of cell division had reduced by 22 per cent and the rate of programmed cell death had approximately doubled. Mr Brennan believes there will be similar effects in humans.

New Scientist ISSUE 1476 Thursday 10 June 1999

COMMENT: It would certainly seem prudent to avoid all routine absolutely unnecessary ultrasound scans for fetal observation. There appears to be more than enough evidence to warrant this recommendation. Pregnancy complications are another issue and one would have to weigh all the factors individually when attempting to determine the benefit/risk ratio.