How Ultrasound Works

Ultrasound is a form of energy and radiation, but not ionizing radiation. Like other sources of energy, it occurs in sound

waves which move at frequencies higher than the human ear can hear. The ultrasound waves are emitted at 2 to 4 megahertz which is a higher frequency than AM radio. The waves bounce off of the internal organs and are interpreted by the scanners which produce a picture on a TV-type screen. The transducer or scanner produces the sound waves and sends them out. It also reads the bounced waves. There are three types of ultrasound. Ultrasound scanning device, Doptones and External Fetal Monitors.

For maternity care, the ultrasound probe is placed over the abdomen. Sometimes a trans-vaginal or trans-rectal probe will be used and this is shaped so that it can be inserted into the vagina or rectum. The scanning devices that make pictures deliver pulsed waves. These devices are usually used for a short period of time. Real time ultrasound is most frequently used. This type of ultrasound makes many pictures of the image being scanned, similar to movie film, and can show fetal activity and how the baby is positioned and the number of babies visible.

An extremely uncommon type of ultrasound is the Doppler. It gives sound only as the sound waves are reflected from the baby's heart. Some Dopplers have earphones that only the practitioner can hear. Others use an amplifier so that the heartbeat is heard aloud. Electronic Fetal Monitors are used most frequently in a hospital setting during labor and delivery. Like the Doppler, it delivers a continuous stream of waves. If continuous fetal monitoring is done, the EFM may be hooked up for yours.