Ultrasound images during pregnancy have helped erase much of the guesswork that formerly challenged those of us who practiced obstetrics. As time has passed, the images have become much sharper and more sophisticated. However, there is still much that is not known about the long term risks of exposure of the unborn to ultrasound.
Fetal ultrasound uses sound waves to make pictures of the fetus and placenta inside the uterus. Since its introduction in the late 1950s, ultrasonography has become increasingly useful. Current real-time scanners depict a continuous picture of the moving fetus on a monitor screen. Very high frequency sound waves ... are generally used for this purpose.
... Some small studies have suggested possible ill-effects of fetal ultrasound. These problems have included low birth weight, speech and hearing problems, brain damage, and non-right-handedness. However, these problems have not been confirmed or substantiated in larger studies from Europe.
There are some people who suggest that ultrasound use in pregnancy contributes to the increase in autism diagnosed in recent years. The complexity of some of the studies and concerns have made the observations difficult to interpret.
... the greatest risk arising from the use of ultrasound is the possible over- and under-diagnosis brought about by inadequately trained or under-experienced technicians, especially if working in relative isolation and/or using poor equipment.
Ultrasound scans should best be performed when there is a clear indication to do so. When that is the case, it is safe to use prudently.