Fetal Doppler Monitor
A Doppler fetal monitor is a hand-held ultrasound transducer used to detect the fetal heartbeat for prenatal care. It uses the Doppler effect to provide an audible simulation of the heartbeat. Some models also display the heart rate in beats per minute (BPM). It’s use is sometimes known as Doppler auscultation (Wikipedia).
The fetal Doppler operates in a fashion similar to those of acoustic fetal stethoscopes as it generates audio output – albeit electronic, with the fetal heartbeat heard by other than the user. It however possesses greater complexity and cost, similitude of an electronic device.
It belongs to a family of perinatal medical devices. As the term implies, a fetal doppler documents the heart rate of a fetus, and the contractions of a mother at term. A normal fetal heart rate is a strong and regular beat of between 120 and 160 per minute.
A high-end fetal Doppler is especially useful during labor as it records the heart rate of the fetus, and the contractions of the mother, thereby informing the midwife/obstetrician of incidences of fetal distress – the result is a reduction in preventable perinatal deaths by opting for Caesarean section.
Fetal heart rate changes slightly in the heat of labor, but drastic changes in heart rate before or after maternal contraction is an indicative factor for fetal distress – failure to heed the warning signal by immediately carrying out a Caesarean section could spell doom for both parties involved.
Component Parts of a Fetal Doppler Monitor
Maternal contractions are measured with a Tocograph, either in the form of a strain gage transducer mounted externally or a belt containing a strain gage. Repositioning is required as labor progresses to assure accurate readings.
Virtually all of the fetal heart rate transducer types, including Surface electrodes and Scalp electrodes require the most minimal testing procedure as these devices can be used to measure your own heart rate. The fetal doppler probe produces ultrasonic pressure waves at about 2.5 MHz with sound as the output.
Check that the Doppler probe works when placed on your chest near your heart – this you are to carry out using the appropriate conductive gel. With a bad probe, no sound is heard even when a stethoscope indicates that a heartbeat exists.
If the doppler refuses to power up, it may be as a result of dead/absent battery, or no power supply from the mains. You may also check for the presence of a broken fuse.
Query the accuracy of both the digital display and the paper trace by comparing their output with a measure of your own heart rate from a watch. Their readings should be within 1 or 2 beats per minute of the correct rate.
To check for effectiveness in maternal contraction monitor, press on the transducer gently at a steady rate of one every minute using a timer. An approximate representation of your applied pressure and rate indicates that your fetal doppler monitor is in excellent condition and can be put into use.
Inaudible sound may result from clogging of conductive gel or broken connection in the speaker – in either of the cases, you should replace the speaker.