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Using Fetal Heart Sounds

Fetal heart sounds is a mode that allows the user and the patient to hear the sound of the fetus's heart and simultaneously displays the pulsed wave spectrum. Fetal heart sounds is available in the OB 2/3 preset for iQ+ users in the US and Canada.

When using Fetal Heart Sounds, you can:

  • View and adjust the position of the sample volume by holding and dragging the gate.
  • Listen to the sound of the fetus’s heart when audio is enabled.
  • Switch between live audio playing and live B-mode by touching the Start Audio/Update B-mode button.
  • Adjust volume of the fetus's heart sound and the gain of spectral trace by dragging finger left and right on the trace while trace is live.
  • Adjust the Scale to optimize for high or low flow by touching the Low Flow/High Flow control in the middle of the screen. Note that the control defines your current state.
  • Adjust the Scroll Speed of the Fetal Heart Sounds trace by touching the Slow Scroll/Fast Scroll control in the middle of the screen. Note that the control defines your current state.

In order to adjust the Gain and Depth of the B-mode reference image, exit Fetal Heart Sounds and optimize the image in the B-Mode.

Placing the Sample Volume

  1. While scanning, enter the OB 2/3 preset.
  2. Under Actions, select the Fetal Heart Sounds mode.
  3. Hold and drag the sample volume gate (the square region along the Doppler line) to the desired location within the fetus’s heart.
  4. Once positioned, tap “Start Audio” to start both the fetal heart sound and the spectral trace. If you do not see a trace or hear a sound, adjust the position of the sample volume.
  5. To adjust the position of the sample volume:
    1. Hold and drag the sample volume gate, which will automatically pause the spectrum and restart B-mode reference image.
    2. Tap the Update B-mode button to manually pause spectrum and restart B-mode.
  6. To adjust scroll speed of trace, tap the “Slow Scroll/Fast Scroll” button.
  7. To adjust the velocity scale, tap the button Low Flow/High Flow button or drag baseline.
  8. To add annotations or measurements, freeze the image and select annotations or measurements.
    1. Note: Annotations and measurements may only be added to the Spectral trace region.
  9. Velocity measurements will be represented in cm/s.
  10. The difference in time between the left and right ends of the caliper will be represented as time (t) in seconds.
  11. To save a Pulsed Doppler image, freeze then press the capture button.

To calculate fetal heart rate (FHR):

  1. While scanning, enter the OB 2/3 preset.
  2. Under Actions, select the Fetal Heart Sounds mode.
  3. Hold and drag the sample volume gate (the square region along the Doppler line) to the desired location within the fetus's heart.
  4. Once positioned, Tap "Start Audio" to start both the fetal heart sound and the spectral trace. If you do not see a trace or hear a sound, adjust the position of the sample volume.
  5. To measure the fetal heart rate, freeze the image and select linear measurements.
  6. Position the calipers of the linear measurement on two successive peaks of the heart cycle (one cardiac cycle). The resulting measurement will show both the heart rate and the time difference between those two peaks.

Note: In accordance with AIUM, The use of Doppler ultrasound during the first trimester is currently being promoted as an aid for screening and diagnosis of some congenital abnormalities. The procedure requires considerable skill and subjects the fetus to extended periods of relatively high ultrasound exposure levels. Due to the increased acoustic output of spectral Doppler ultrasound, its use in the first trimester should be viewed with caution. Spectral Doppler imaging should only be used when there is a clear benefit/risk advantage, and both the TI and examination duration are kept low. Protocols that typically involve TI values lower than 1.0 reflect minimal risk.

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