Ultrasound scanning in pregnancy is used to detect the fetus's heartbeat and obtain other information. A technician applies a gel to a woman's abdomen and scans the abdomen with a handheld device called a transducer. The gel enhances the transmission of sound waves, which are produced by the transducer. The sound waves reflect off internal structures and the fetus, and the pattern of this reflection can be displayed on a video monitor.
Video from Center for Biomedical Communications, College of Physicians and Surgeons, Columbia University.