How does a fetal doppler work

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Fetal doppler or fetal heart rate monitor is a handheld device which is used to listen to the baby’s heartbeat inside the womb of the mother. Fetal doppler works on the principle of Doppler effect, discovered in 1842 by a famous Austrian mathematician and physicist Christian Doppler (1803-53). Doppler discovered that when high-frequency sound waves are reflected from a moving object, their frequency change and this can be analyzed.

Each fetal doppler contains a transducer or a probe which sends out short pulses of ultrasound sound waves into the directed area of the body. When these sound waves are reflected from the baby’s beating heart, their frequency change. When this echo is received by the fetal doppler, it converts this signal into the baby’s heartbeat. Normally a speaker or an auxiliary jack of earphones is connected to the doppler through which one can hear the heartbeat.

Fetal doppler and Ultrasound machine used by doctors work on the same doppler effect. The main difference between a fetal doppler and an ultrasound machine is that the waves emitted from an ultrasound machine are much higher and stronger (over many times higher) than those emitted from a fetal doppler. Moreover, the frequency and variation of probe use (between 2,5 -10 MHZ) and output levels of up to 740 Watts means that only a trained ultrasound technician can use an Ultrasound machine. On the other hand, a fetal doppler having only a few probes (2, 3, 4MHZ) and very low output levels of 20Watts makes it safe and easy to use by anyone at home. However, the person should follow the guidelines on the safe usage of the fetal doppler. Please note that use of a fetal doppler doesn’t substitute regular doctor visits. You should always consult with your doctor and midwife regarding usage of fetal doppler.

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