LONDON
- Swedish scientists have uncovered evidence suggesting that ultrasound scans
on pregnant women can cause brain damage in their unborn babies.
In the most comprehensive study yet on the effects of the scanning, a team of
doctors found that men born to mothers who underwent scanning were more likely
to show signs of subtle brain damage.
Professor Juni Palmgren, a team member from the Karolinska Institute in
Stockholm, said: "I would urge people not to refuse to have ultrasound
scanning, as the risk of brain damage is only a possibility -- but this is an
interesting finding and needs to be taken seriously."
The implications of the study are to be raised at an international meeting of
scientists this week in Edinburgh. There have been calls for urgent further
research.
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 the Swedish team 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% 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% increase in risk of left-handedness among boys
pre-natally exposed to ultrasound," they say. "If this association
reflects brain injury, this means as many as one in 50 male fetuses pre-natally
exposed to ultrasound are affected."
Dr. Carl Nimrod, chairman of obstetrics and gynecology at the University of
Ottawa, emphasized that the research should be seen in context. "If the
research was sound, et cetera, at best one could say there is an association
between left-handedness and exposure to ultrasound, but there's a big difference
between an association and a causation," he said.
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 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 would carry a risk of
causing cancer.
Normally, left-handedness is genetic: The likelihood of two left-handed parents
having a left-handed child is 35%, while for two right-handed parents, it is
only 9%.
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 5% in the 1920s to 11% today.
Researchers have estimated that only 20% 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."
Beverley Beech, the chairwoman of Britain's 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," Ms. Beech said. "We should be advising women to think
very, very carefully before they have scans at all."