THURSDAY, Dec. 20, 2001 (HealthDayNews) -- Ultrasound imaging has been considered completely safe, providing doctors with a wealth of information about what's going on inside the body. But new research suggests that the sound wave test may not be harmless after all.
A recent study from the Karolinska Institute in Sweden found that babies of mothers who underwent ultrasounds in the 1970s were more likely to be born left-handed than those whose mothers did not have the exam.
The researchers say the finding suggests that sonography somehow disrupts normal brain development. Other experts, however, are not convinced.
Ultrasound devices transmit high-frequency sound waves into the body through a transducer. When the sound waves encounter an object, they bounce back to the transducer. An image is formed as the machine calculates how long it takes each sound wave to bounce back.
Because of its record of safety and its usefulness in
assessing the size and health of unborn babies, almost every pregnant woman in the United States undergoes at least one ultrasound scan.
For this study, the researchers gathered data about almost 180,000 Swedish men who were entering the military. About 7,000 of them had been exposed to ultrasound in utero, while 172,537 had not. The researchers say they tried to control for maternal age, preterm birth and low birth weight, factors that previous studies have shown affect left- or right-handedness.
The researchers say 8 percent to 9 percent of people usually are left-handed. The study found that the young men in the study who had been exposed to ultrasound had a 32 percent higher chance of being left-handed.
"It's a nominal increase," says Paul Visintainer, an epidemiologist and program director for quantitative health sciences at New York Medical College, in Valhalla, N.Y. "But, the study raises a good point. We can't just assume that these medical procedures are without consequence."
The findings appear in a recent issue of the journal Epidemiology.
Visintainer says the study was large and well done, but he says factors other than ultrasound may be involved. He says other medical procedures could account for the results. Or, he says the women who had ultrasounds may have had conditions that affected the results.
Dr. Boris Petrikovsky, professor of obstetrics and gynecology at New York University School of Medicine, says mostly high-risk patients received ultrasound scans in the 1970s. So, he says, "There was already a bias."
Petrikovsky also questioned the conclusion that being left-handed is a marker of abnormal brain development. "There is no evidence that being left-handed is associated with brain damage," he says.
Dr. Edmund LaGamma, professor of pediatrics at New York Medical College and director of the division of newborn medicine at Westchester County Medical Center, also in Valhalla, says he believes the results are a "statistical aberration." He says it doesn't seem biologically plausible that ultrasound could so selectively affect the brain.
"How can it be so selective that it only affects handedness -- not cognition, not speech?" he asks.
What To Do
So, where does that leave pregnant women who are scheduled for ultrasound? LaGamma and Petrikovsky say they don't need to worry. "The vast preponderance of evidence is that there is no impact on fetal outcome," says LaGamma.
But, Petrikovsky says that doesn't mean you should have an ultrasound just to see your baby's face or to learn the sex of your child. He says the tests are expensive and should be used only when medically indicated.
For more information on ultrasound use during pregnancy, go to the University of Michigan Health System.
To read about the technology behind ultrasound, go to HowStuffWorks.com.
