ABSTRACT: Diagnostic ultrasound of the pulse-echo imaging type is used in at least 25 per cent of pregnancies, and Doppler continuous wave ultrasound, as employed in external electronic fetal monitors, is used in nearly all pregnancies. Diagnostic ultrasound energy levels are from 0.1 to 40 mW/cm2. These intensity levels depend on the characteristics of the ultrasonic beam and temporal exposure. The American Institute of Ultrasound in Medicine states that…“there have been as of October, 1982 no independently confirmed significant biological effects in mammalian tissues exposed to intensities below 100 mW/cm2.” Some of the animal studies reviewed by the AIUM to reach this conclusion are discussed.