Ultrasound Safety in Obstetrics

Current developments in international standards and changes in the regulation of medical ultrasound will allow greater control of higher power diagnostic equipment by the ultrasonologist. This brings a responsibility for risk/benefit assessment that requires an understanding of the potential biological effects and the margin of safety for each kind of ultrasound procedure. The development of new, sophisticated diagnostic ultrasound systems has been accompanied by a continuing trend of increasing power outputs. The relaxation of intensity limits for premarket approval by the Food and Drug Administration allows substantially increased intensity of ultrasound to be delivered to the fetus. Modern diagnostic equipment operating at maximum output conditions can produce significant biological effects in mammalian tissues. Substantial increases in temperature have been consistently recorded when the pulsed Doppler ultrasound beam encounters bone in either transcraniator fetal exposures. However, there is no risk of adverse heating effects from ultrasound scanning procedures using simple B-mode. A number of studies have recently reported ultrasound-induced hemorrhagic lesions in tissues of lungs and intestines in mammals following brief exposure to the maximum operating conditions in diagnostic equipment. The effect depends on the presence of a tissue/air interface, thus suggesting it is unlikely to have clinical significance in obstetrical ultrasound examinations. The implications to human health are not fully understood.