WASHINGTON — Exposure to ultrasound can affect
fetal brain development, a new study suggests. But researchers say the
findings, in mice, should not discourage pregnant women from having
ultrasound scans for medical reasons.
When pregnant mice were exposed to ultrasound, a
small number of nerve cells in the developing brains of their fetuses
failed to extend correctly in the cerebral cortex.
"Our study in mice does not mean that use of
ultrasound on human fetuses for appropriate diagnostic and medical
purposes should be abandoned," said lead researcher Pasko Rakic,
chairman of the neurobiology department at Yale University School of
Medicine.
However, he added in a telephone interview, women should avoid unnecessary ultrasound scans until more research has been done.
Dr. Joshua Copel, president-elect of the American
Institute of Ultrasound Medicine, said his organization tries to
discourage "entertainment" ultrasound, but considers sonograms important
when there is a medical benefit.
"Anytime we're doing an ultrasound we have to
think of risk vs. benefit. What clinical question are we trying to
answer," Copel said in a telephone interview. "It may be very important
to know the exact dating of pregnancy, it's certainly helpful to know
the anatomy of the fetus, but we shouldn't be holding a transducer on
mom's abdomen for hours and hours and hours."
Rakic's paper said that while the effects of
ultrasound in human brain development are not yet known, there are
disorders thought to be the result of misplacement of brain cells during
their development.
"These disorders range from mental retardation
and childhood epilepsy to developmental dyslexia, autism spectrum
disorders and schizophrenia," the researchers said.
Their report is in Tuesday's edition of Proceedings of the National Academy of Sciences.
Early ultrasound scans are done to determine the
exact week of the pregnancy and they are also done later to check for
anatomical defects and other problems.
However, some expectant parents have sought scans
to save as keepsakes even when they were not medically necessary, a
practice the Food and Drug Administration discourages.
The Institute of Ultrasound Medicine was
particularly concerned last year when it was announced that actor Tom
Cruise had purchased an ultrasound machine for his pregnant fiancee,
Katie Holmes, so they could do their own sonograms.
"Purchase of an ultrasound machine for private,
at home use entails inappropriate operation of a prescription medical
device designed for diagnostic use by a trained medical professional,"
the group said in a statement issued at the time.
Copel, a professor of obstetrics and gynecology
at Yale University School of Medicine, did point out that there are
large differences between scanning mice and scanning people.
For example, because of their size, the distance
between the scanner and the fetus is larger in people than mice, which
reduces the intensity of the ultrasound. In addition, he said, the
density of the cranial bones in a human baby is more than that of a tiny
mouse, which further reduces exposure to the scan.
The paper noted that the developmental period of
these brain cells is much longer in humans than in mice, so that
exposure would be a smaller percentage of their developmental period.
However, it also pointed out that brain cell
development in people is more complex and there are more cells
developing, which could increase the chances of some going astray.
In Rakic's study, pregnant mice were exposed to
ultrasound for various amounts of time ranging from a total exposure of 5
minutes to 420 minutes. After the baby mice were born their brains were
studied and compared with those of mice whose mothers had not been
exposed to ultrasound.
The study of 335 mice concluded that in those
whose mothers were exposed to a total of 30 minutes or more, "a small
but statistically significant number" of brain cells failed to grow into
their proper position and remained scattered in incorrect parts of the
brain. The number of affected cells increased with longer exposures.
The research was funded by the National Institute of Neurological Disorders and Stroke.
Here is another great article on the subject:
