Risks Of Ultrasound
Many doctors, as well as patients, assume that ultrasound is a completely innocuous procedure for the fetus, especially when compared to the known risks of X-rays to the fetus during pregnancy.
Although the best evidence to date indicates no harmful effects of ultrasound exposure to the fetus, no studies have had a long enough follow-up to detect conditions in which there are long latent periods, such as cancer. There still remains the possibility of more subtle side effects that may not show up for ten or 20 years or even until the next generation.
A number of animal studies showed developmental, blood, nervous system, immune and chromosomal effects on fetal animals whose mothers were exposed to ultrasound in pregnancy. However, evidence from animal studies is conflicting and much of it has not been confirmed by other researchers.
At present, there is no good evidence that ultrasound causes harmful genetic effects such as mutation or chromosome breakage. On the other hand, the possibility that ultrasound exposure causes chromosome damage cannot be ruled out.
As Neilson and Grant say, in their chapter on ultrasound in EFFECTIVE CARE IN PREGNANCY AND CHILDBIRTH, (Oxford University Press, 1989), "There has been surprisingly little well organized research to evaluate possible adverse effect of ultrasound exposure on human fetuses." As far as I know, there is little future research planned on this important area.
So far, studies on human children have not verified any harmful effects. However, it is worth noting that research on ultrasound and its safety is on a level similar to where we were before 1950 with the risk of X-rays to newborns.
As Dr. Bernard Ewigman, says in Journal Of Family Medicine (Vol 29 Jun\89):
"Following several decades of use, adequately designed studies showed a twofold to threefold increased risk of leukemia in children with fetal X-ray exposure, for an incidence of one in 5,000. No current study of ultrasound exposure has an adequate sample to rule out an adverse consequence of even one in 2,000... The lack of direct evidence linking human fetal ultrasound with adverse outcomes in existing studies, although reassuring, cannot be interpreted to mean there is no risk."
The European Committee for Ultrasound Radiation Safety concluded there were no short term growth defects in children after 20 years of using US.
Two well designed studies checked to see if there was a relationship between ultrasound exposure and childhood cancer. Both showed there was no difference in the cancer rates of children who had been exposed to ultrasound and those that weren't. However, one of the studies showed that children over five dying of leukemia or other cancers were more likely to have been exposed to ultrasound.
To date, there have been only two large scale human studies on the long-term effects of ultrasound on children who have been exposed during pregnancy.
At the University of Colorado, 1,600 children whose mothers were exposed to ultrasound and 1,600 children whose mothers were not exposed to ultrasound were studied. From this large group, Dr. Charles Stark was able to trace and examine only 425 exposed and 381 unexposed children at seven and 12 years of age. The only difference he noted in the exposed children was an increased incidence of dyslexia, and an increased rate of hospitalizations.
At the University of Manitoba in Winnipeg a similar study was carried out with 10,000 exposed children and 5,000 unexposed children. Preliminary reports on this study showed no evidence of increased abnormalities, speech and hearing disorders, cancer or developmental or growth problems in children who were exposed to US while in the womb.
So far only one report on this study has been published. Dr. Lyons, the Director of the Section of Diagnostic Ultrasound at the University of Manitoba and his colleagues followed 149 pairs of siblings, one of whom had been exposed to ultrasound and the other who had not.
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