![]() ![]() By pressing the freeze button, one can then use the caliper function to measure the fetal heart rate. The waveform represents the movement of the beating heart. Generally one is able to see a faint sinusoidal wave across the M-Mode screen. ![]() The resulting image is a representation of the movement as seen through the single M-mode cursor beam. Using the trackpad or mouse ball, place the beam over the best view of the beating heart. In actual bedside practice, first visualize the beating fetal heart on the screen (with trans-abdominal or transvaginal scanning, with preset changed to OB setting), then press M-Mode this brings up a single M-Mode cursor beam. In brief, M-Mode gives a real-time representation of a moving object. When visualizing a developing pregnancy, think of using “ Mommy-Mode.” This is an easy way to recall the need for M-Mode imaging. Particularly, investigations with laboratory animals have documented that pulsed (Doppler) ultrasound can cause elevations in temperature and damage biological tissues in vivo. Although not studied well in humans, inadvertent and prolonged use of pulse-wave Doppler may have adverse effects on the unborn fetus. This is a rather easy US skill to acquire, but the measurement must be done with the M-Mode, not pulse wave Doppler: see Image #1 – incorrect use of Doppler and image #2 – correct use of M-Mode. As commonly practiced, the pregnant patient has an additional vital sign – assessment of the fetal heart rate. ![]() The image of the week focuses on fetal heart rate determination. ![]()
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