Location of the placenta. ...... 19 out of 20 women who have placenta previa detected on RPU will be needlessly worried, as the placenta will effectively move upwards as the pregnancy progresses.12 Furthermore, detection of placenta previa by RPU has not been found to be safer than detection in labor.13......................................
Reasons for Concern
Ultrasound waves are known to affect living tissues in at least two ways. First, the sonar beam heats the highlighted area by about 1°C (2°F). This is presumed to be insignificant, based on whole-body heating in pregnancy, which seems to be safe up to 2.5°C (5°F).21 The second effect is cavitation, where the small pockets of gas that exist within mammalian tissue vibrate and then collapse. In this situation "...temperatures of many thousands of degrees Celsius in the gas create a wide range of chemical products, some of which are potentially toxic."22 The significance of cavitation in human tissue is unknown.
A number of studies have suggested that these effects are of real concern in living tissues. The first study indicating problems analyzed cells grown in the lab. Cell abnormalities caused by exposure to ultrasound were seen to persist for several generations.23 Another study showed that, in newborn rats (who are at a similar stage of brain development as humans at four to five months in utero), ultrasound can damage the myelin that covers nerves,24 indicating that the nervous system may be particularly susceptible to damage from this technology.