By Robert Matthews
Epidemiology December 2001 12:618
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