Lefties: are they born that way?

A surprising new study suggests a weak link between ultrasound exposure in the womb and the tendency to lefthandedness later in life.

Although obstetricians consider ultrasound during pregnancy safe, some concerns linger about this common procedure. Researchers have shown that ultrasound isn't associated with severe birth defects, yet some scientists still worry about subtle types of brain damage.

Last year, a Norwegian team led by Kjell Salvesen of the University of Trondheim found no evidence that in utero exposure to ultrasound increased the risk of learning disabilities in school-age children (SN: 4/4/92, p.218). Now, that team has offered another view of ultrasound's fetal effects.

The Norwegian researchers studied 2,161 children born in the cities of Trondheim and Alesund from 1979 to 1981. Approximately half the kids had been exposed to ultrasound during gestation. The other children had no such exposure.

During the children's first year of life, the researchers put them through a battery of tests designed to assess neurological functioning. They found no clear differences between the ultrasound-screened kids and their peers.

While that's reassuring news, Saivesen's team did find a weak association between ultrasound exposure in the womb and the chances of being a leftie by age 8 or 9. That link appeared independent of a family history of left-handedness.

However, those findings could be the result of chance, the team ciutions in the July 17 BRITISH MEDICAL JOURNAL.

Alternatively, they say, the sound waves employed by ultrasound scanners may influence the migration of neurons in the developing fetus. Changes in fetal brain formation could cause a child to favor its left rather than its right hand. Although the new study hints at this scenario, further research must be done to prove ultrasound's influence on brain development.