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By Robert Matthews
Evidence suggesting that ultrasound scans
on pregnant women cause brain damage in their unborn babies
has been uncovered by scientists.
In the most comprehensive study yet on
the effect of the scanning, doctors have found that men born
to mothers who underwent scanning were more likely to show
signs of subtle brain damage.
During the 1990s, a number of studies
hinted that ultrasound scanning affected unborn babies. Research
has suggested that subtle brain damage can cause people who
ought genetically to be right-handed to become left-handed.
In addition, these people face a higher risk of conditions
ranging from learning difficulties
to epilepsy.
Now a team of Swedish scientists has confirmed
the earlier reports on the effects of ultrasound with the
most compelling evidence yet that unborn babies are affected
by the scanning. They compared almost 7,000 men whose mothers
underwent scanning in the 1970s with 170,000 men whose mothers
did not, looking for differences in the rates of left- and
right-handedness.
The team found that men whose mothers
had scans were significantly more likely to be left-handed
than normal, pointing to a higher rate of brain damage while
in the womb. Crucially, the biggest difference was found among
those born after 1975, when doctors introduced a second scan
later in pregnancy. Such men were 32 per cent more likely
to be left-handed than those in the control group.
Reporting their findings in the journal
Epidemiology, the researchers warned that scans in late pregnancy
were now routine in many countries.
The present results suggest a 30
per cent increase in risk of left-handedness among
boys pre-natally exposed to ultrasound. If this association
reflects brain injury, this means as many as one
in 50 male fetuses pre-natally exposed to ultrasound are affected.
Other doctors and scientists caution that
until further studies are carried out, scanning should still
be regarded as safe by mothers-to-be. If confirmed, however,
the findings would mean that ultrasound scans are causing
slight brain damage in thousands of babies in Britain each
year.
Ultrasound scans, which were introduced
in the 1960s, have long been regarded as a safe means of checking
on the health of unborn children. The scanners use high-frequency
sound waves to give X-ray-like images of the inside of the
womb, but without using radiation, which carries a risk of
causing cancer. Between the 1960s and today, the number of
pregnant women having scans in western Europe has increased
from a handful to virtually all of them.
Normally, left-handedness is genetic:
the likelihood of two left-handed parents having a left-handed
child is 35 per cent, while for two right-handed parents,
it is only nine per cent. It is when the incidence of left-handedness
begins to rise above these normal rates that scientists become
concerned that brain damage of some kind could be a factor.
Other surveys have shown that premature
babies are five times more likely than normal to be left-handed.
According to the Swedish researchers, the human
brain undergoes critical development until relatively late
in pregnancy, making it vulnerable to damage. In addition,
the male brain is especially at risk, as it continues to develop
later than the female brain.
The growing evidence that ultrasound affects
unborn babies may cast new light on the puzzling rise in left-handedness
over recent years.
In Britain, the rate has more than doubled,
from five per cent in the 1920s to 11 per cent today. Researchers
have estimated that only 20 per cent of this rise can be put
down to the suppression of left-handedness among the older
generation.
Dr Francis Duck of the British Medical
Ultrasound Society will chair a discussion of the results
at the international meeting of ultrasound experts being held
this week in Edinburgh. "When the first study suggesting
a link came out, it was possible to ignore it, but now this
is the third," he said. "What it demonstrates is
the need to investigate the link further, and to look at possible
mechanisms."
Dr Duck cautioned, however, that ultrasound
scanning has saved the lives of countless babies: "This
research must be seen in context, and it should not deter
anyone from having an antenatal scan."
Beverley Beech, the chairman of the Association
for Improvements in Maternity Services, criticized doctors
for insisting for years that ultrasound was totally safe.
"I am not sure at all that the benefits
of ultrasound scans outweigh the downsides," said Ms
Beech. "We should be advising women to think very, very
carefully before they have scans at all."
www.news.telegraph.co.uk
December 9, 2001
Epidemiology
December 2001 12:618
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