The NCRP recommends that ultrasound machine operators be particularly aware that risks may
offset the benefits of ultrasound exposures to the fetus when the temperature rise at the focal point of the
ultrasound beam is calculated to be more than 3 degrees Celsius for ten minutes or more. However, in
clinical practice it would be unusual for ultrasound to raise the temperature of any part of the fetus
significantly for 10 minutes or longer.