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The Boston Medical Center study included 107 children with autism and 313 without the disorder and found no association between autism risk and the number or length of ultrasounds the children's mothers had during pregnancy, CNN reported.
But the researchers did say they found a statistical association between autism and deep ultrasound wave penetration during the first and second trimesters, according to the study published Monday in the journal JAMA Pediatrics.
"Depth of penetration has to do with the distance between the ultrasound transducer (probe) on the skin and the point at what you're looking at on the ultrasound," study co-author Dr. Jodi Abbott explained.
But depth of penetration is the farthest down the ultrasound beam reaches, according to an expert who was not involved in the study.
"It has nothing to do with where the fetus and his/her parts are. The depth could indicate 20 centimeters and the fetus be at 12 centimeters," Dr. Jacques Abramowicz, chair of the safety committee of the World Federation of Ultrasound in Medicine and Biology, told CNN.
"As the ultrasound penetrates the tissues, it actually loses energy," Abramowicz said. "The difference between the groups of children is minimal in terms of the depth. And clinically not significant."
Study first author Dr. N. Paul Rosman, a pediatric neurologist, stressed that an association does not prove cause and effect, meaning that the study findings do not mean ultrasound causes autism.
He said the study should be viewed "critically" because it did examine a number of factors that might affect a fetus, including whether the mother became ill or smoked during pregnancy, CNN reported.
"We think this study was done well, but there are deficiencies, and that's why we call for additional studies," Rosman said.
Other experts said no firm conclusions can be drawn from the study because its methodology was not rigorous enough, CNN reported.
Other researchers say that the methodology of the study was not rigorous enough to draw firm conclusions and that pregnant women should not have concerns about undergoing a medically necessary ultrasound exam.
"Unfortunately, the authors do not appear to know what is meant by the ultrasound penetration depth. It does not relate to the amount of ultrasound entering the body," Dr. Marvin Ziksin, a professor of radiology and medical physics at Temple University, told CNN.
"The factors that determine the amount of ultrasound entering the body, and what would affect the fetus, are the mechanical index, the thermal index, and ultrasound power and intensity, for which no significant differences were found," Ziskin explained. "The amount of ultrasound imparted into pregnant patients has no association with autism spectrum disorder."
The experts not involved in the research also took issue with the study authors' claim that ultrasound technology is "minimally regulated," CNN reported.
"It is extremely regulated, particularly in the United States, with the Food and Drug Administration looking very closely at the machines." Abramowicz said.
It is true that the use of ultrasound is less regulated, but any patient whose ultrasound exam is done by a qualified medical technician is safe.
However, Abramowicz agrees with the American Pregnancy Association that pregnant women should never get a "keepsake" ultrasound from the growing number of services in shopping malls or other commercial locations in the U.S.
The new study does not provide "enough evidence to make a recommendation for or against ultrasound," Thomas Frazier, chief science offers of Autism Speaks, told CNN.
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