Fetal Heart Beat - Clinical

If you use a Doppler ultrasound fetal heartbeat detector, you can usually hear the heartbeat by 12-14 weeks gestation.

You aren't really hearing the heartbeat but the amplified "beat frequency" generated by the interaction of the outgoing ultrasound signal, and the returning ultrasound signal. When the outgoing signal is reflected back by a moving object (fetal heart), then the returning signal has a slightly higher frequency (if the object is moving toward the transducer), or slightly lower frequency (if the object is moving away). This is called the Doppler shift. Every so often, the peaks and valleys of these slightly different frequencies are superimposed on each other, creating a much louder sound, that happens to be in the audible range. It is this sound that you are hearing.

The normal rate is generally considered to be between 120 and 160 beats per minute.

• The rates are typically higher (140-160) in early pregnancy, and lower (120-140) toward the end of pregnancy.
• Past term, some normal fetal heart rates fall to 110 BPM.
• There is no correlation between heart rate and the gender of the fetus.

1. Use a coupling agent (Ultrasound gel, surgical lubricant or even water) to make a good acoustical connection between the transducer and the skin.
2. Doppler fetal heartbeat detectors are moderately directional, so unless you happen to aim it directly at the fetal heart initially, you will need to move it or angle it to find the heartbeat.
3. Confirm a normal rate, and listen for any abnormalities in the rhythm of the fetal heart beat.

Using a DeLee stethoscope (equipped with a head-mount), you can sometimes hear the heartbeat by 16 weeks but unless you are practiced with it, you won't hear it until 20 weeks, at which time the mother can usually tell you that she feels the baby moving Using a conventional stethoscope, you may never hear the fetal heartbeat

DeLee Stethoscope

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