Ultrasound is a scanning technique used to image the growing fetus. The transducer portion emits inaudible sound waves, which fan out as they travel through your abdomen. When they hit dense structures like the fetus and the wall of your uterus, the sound waves bounce back to the transducer and are translated into a visual image by the computer.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.