WASHINGTON (AP) -- Keepsake sonograms have become a popular item with many young parents -- from Tom Cruise to the couple next door. But it's a practice some physicians would like to discourage. The latest concern comes from a study that suggests, in mice at least, that ultrasound can affect the development of the fetal brain. But researchers said the findings should not keep pregnant women from having ultrasound scans when needed for medical reasons. When pregnant mice were exposed to ultrasound, some 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 Dr. Pasko Rakic, lead researcher and chairman of the neurobiology department at Yale University School of Medicine. However, he added, 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. "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 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 Cruise had purchased an ultrasound machine so he and his pregnant fiancee, Katie Holmes, 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 then. Copel, a professor of obstetrics and gynecology at Yale University School of Medicine, did point out 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 cranial bones in a human baby are denser than those of a tiny mouse, which further reduces exposure to the scan. The paper noted the developmental period of these brain cells is much longer in humans than in mice, so exposure would be a smaller percentage of the 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.

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