It has been over 40 years since ultrasound was first used on pregnant women. Unlike X-rays, ionizing irradiation is not present and embryotoxic effects associated with such irradiation should not be relevant. The use of high intensity ultrasound is associated with the effects of "cavitation" and "heating" which can be present with prolonged insonation in laboratory situations.
Although certain harmful effects in cells are observed in a laboratory setting, abnormalities in embryos and offsprings of animals and humans have not been unequivocally demonstrated in the large amount of studies that have so far appeared in the medical literature purporting to the use of diagnostic ultrasound in the clinical setting. Apparent ill-effects such as low birthweight, speech and hearing problems, brain damage and non-right-handedness reported in small studies have not been confirmed or substantiated in larger studies from Europe. The complexity of some of the studies have made the observations difficult to interpret. Every now and then ill effects of ultrasound on the fetus appears as a news item in papers and magazines. Continuous vigilance is necessary particularly in areas of concern such as the use of pulsed Doppler in the first trimester.
The greatest risks arising from the use of ultrasound are the possible over- and under- diagnosis brought about by inadequately trained staff, often working in relative isolation and using poor equipment.
It should be bornt in mind that prenatal ultrasound cannot diagnose all malformations and problems of an unborn baby (reported figures range from 40 to 98 percent), so one should never interpret a normal scan report as a guarantee that the baby will be completely normal. Some abnormalities are very difficult to find or to be absolutely certain about.
Some conditions, like for example hydrocephalus, may not have been obvious at the time of the earlier scan. The position of the baby in the uterus has a great deal to do with how well one sees certain organs such as the heart, face and spine. Sometimes a repeat examination has to be scheduled the following day, in the hopes the baby has moved.
Images tend also to be strikingly clear in skinny patients with lots of amniotic fluid, and frustratingly fuzzy in obese women, particularly if there is not much amniotic fluid as in cases of growth restriction. As in almost every endeavor, there is also a wide difference in the skill, training, talent, and interest of the sonographer or sonologists. The improvements in equipment has also lead to the earlier detection of abnormal structures in the fetus bringing along with it "false positives" and "difficult-to-be-sure-what-will-happen" diagnosis that could generate huge amount of undue anxiety in patients.