I would urge people not to refuse ultra-sound scanning as the risk of brain damage is only a possibility

Professor Juni Palmgren

However as of yet there is no indication that harm was done to the babies through the scans, according to an article in a journal.

The implications of the study are to be discussed at an international meeting of scientists in Edinburgh this week.

A total of 7,000 men were studied whose mothers had scans in the 1970s and compared with 172,000 men whose mothers had not had scans.

Increased risk

The study suggested scanning produced an extra three left-handed babies per 100 births.

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.

The paper in the journal Epidemology concluded there were some possibilities the ultrasound had affected the brain.

However remote the risk, this was serious enough to merit concern.

The researchers warned: "The present results suggest a 30% increase in risk of left-handedness among boys pre-natally exposed to ultrasound."

"If the association reflects brain injury, this means as many as one in 50 male foetuses pre-natally exposed to ultrasound are affected."

However the research found no harm to the babies had been demonstrated.

Prof Juni Palmgren, of the Karolinska Institute in Stockholm, a member of the team, told The Sunday Telegraph: "I would urge people not to refuse ultra-sound scanning as the risk of brain damage is only a possibility - but this is an interesting finding and needs to be taken seriously."

Later development

According to the Swedish scientists, the human brain undergoes critical development late into a woman's pregnancy.

The male brain is especially vulnerable because it continues to develop later than the female brain.

Many doctors believe ultrasounds, which are used routinely in late pregnancies, have saved countless lives and women should not be deterred from having an antenatal scan.

But Beverley Beech, chairwoman of the Association for the Improvements in Maternity Services, told the paper that women should be fully briefed on the risks of ultrasound and should avoid having scans unless they were essential.