“Hearing the First Heartbeat”

A Review on Edan Sonotrax Fetal Doppler Monitor

For first time parents, nothing compares to the joy that of hearing the heartbeat of their unborn child (in its early stages) brings to them. And that would be impossible if the Doppler fetal monitor was not invented.

A Doppler fetal monitor or Doppler fetal heart rate monitor is a hand-held ultrasound transducer that uses the Doppler Effect to detect the heart beat of a fetus and provides an audible simulation of the heart beat. Some models also display the heart rate in beats per minute. Use of this monitor is sometimes known as Doppler auscultation.

Doppler Fetal: The Origin

The Doppler Effect was discovered by Austrian mathematician and physicist, Christian Doppler (1803-53). Each fetal heart monitor uses a transducer or probe of varying MGHZ (millions of cycles per second), usually 2 or 3, containing piezoelectric crystals which send short sound pulses into the directed area of the body. Every time one of these sound waves is sent the transducer (probe) pauses briefly and listens for the returning echo at which time the fetal heart doppler determines the depth and direction of each returning sound wave and converts the signal into the fetal heartbeat you hear. This heartbeat is not your baby's actual heartbeat but a reproduction.

A Doppler fetal monitor provides information about the fetus similar to the information a fetal stethoscope provides. One advantage of the Doppler fetal monitor over an acoustic (not electronic) fetal stethoscope is the audio output, which allows people other than the user to listen to the heartbeat. One disadvantage is the greater complexity and cost, and lower reliability, of an electronic device.

Originally intended for use by health care professionals, this device is becoming popular for personal use.

On Using Fetal Doppler?

The best way to begin an exam is to be lying down exposing the abdomen, although it may be possible to find the heart rate in a sitting or standing position. Apply a generous amount of ultrasound gel to the fetal doppler probe. Early in pregnancy the best technique is to begin with the transducer (probe) on the midline of the abdomen (above the pubic line) aiming downward behind the pubic bone. The probe should then be angled slowly in search for the fetal heart rate. Be patient, early in pregnancy the size of the fetal heart is so small and the sound so faint it can be very easy to pass over and miss the sounds. A 2mghz probe is best for early detection, standard on Huntleigh FD1+ and D920. A full bladder can make it easier to find the heartbeat. Try to keep from dragging the probe around as it will only increase static and make it more difficult to find the heartbeat.

How to know if you’re hearing your baby's heartbeat and not yours?

The easiest and most conclusive way to decipher your heartbeat from your baby's is by the heart rate or BPM (beats per minute). Your baby's heart rate will be between 120 & 180 BPM. This is considered the normal range of a fetal heart rate. Conversely, your heart rate will be much less 60-100 BPM. Early in pregnancy its normal for the fetal heart rate to vary within a reasonable range. As your pregnancy progresses and your baby grows the heart rate will become more static. Also be aware that like adults your baby's heart rate will vary depending on activity level. If you have further questions or concerns about your baby's heart rate contact your health care provider.

Why do I need ultrasound gel?

Ultrasound gel is imperative when doing and exam with a fetal doppler. Ultrasound gel is specially formulated to act as a coupling agent and reduce static that is often caused when using a fetal doppler. To get optimal use and sound out of a fetal doppler monitor use plenty of gel. Do not use colored gels or lotions. Any oil based substance used with a fetal doppler will cause excess static and can damage the doppler probe. Since the probe is one of the most integral parts of the doppler system they can run upwards of $300 to replace. Use only ultrasound gel.

On the recommended Fetal Doppler Brand in the market

The SonoTrax Fetal Doppler provides a simple, easy to use Ultrasonic Doppler that allows mothers and health care professionals to retrieve a fetal heart rate (FHR) and listen to the sound of the heart beat. This Fetal Doppler provides different easy-to-use modes that provide Real-time FHR display, Averaged FHR, or a manual mode that allows the user to view a fetal heart rate for 10 heart beat period or for 5 heart beat, giving you a calculated measurement with a press of a button.

Sonotrax Lite is for simple auscultation (intermittent listening). Sonotrax Basic is a high performance model with FHR digital LCD display. Sonotrax Pro has backlight and audio playback. All these models have audio output, which can be connected with earphone or recorder. As well, you can operate the unit with 4MHz or 8MHz probe for vascular diagnose.

While Sonotrax Basic is a Doppler Unit with LCD Display, Low battery indication, No back light display or with backlight, Probe Frequency Detection, Your Choice Of Either 2,3,4, or 8 Mhz Waterproof Interchangable Probe, 3 Working Modes (Realtime, Average, Manual) and Normal Carry Case.

And, the Sonotrax Pro is Doppler Unit with LCD Display, Blue Backlight, Battery Indication, Probe Frequency Detection, Your choice of either 2,3,4 or 8 Mhz Waterproof Interchangable Probe, 3 Working Modes (Realtime, Average, Manual) and Normal Carry Case.

Edan Instruments, Inc. is one of the leading medical equipment manufacturers in China. Located in Shenzhen, a major electronic center where talent and productivity converge, Edan is home to more than 500 employees working in R&D, manufacturing and marketing.