FOETAL HEART DETECTOR

Typical Number in Hospital: 10

Cost Bands: 2

References: 1

This is usually an ultrasonic doppler device although early types were low-frequency microphones applied to the maternal abdomen. Ultrasonic types employ a low frequency of ultrasound (e.g 2 MHz) transmitted through the skin as a continuous wave (not pulsed); the echoes returning from the region of the foetal heart are shifted in frequency due to the movement of the walls and valves of the heart and also the blood. The doppler shifts from the transmitted ultrasonic frequency fall mostly in the low audible range and so, by a simple process of frequency subtraction, these doppler frequencies are presented to a loudspeaker. The foetal heart rate can be detected by timing the rate of pulsations, and some information about the placenta can also be gained by the characteristic sound produced by the blood flowing slowly through this organ. Foetal heart detectors of the above type have to some extent replaced the traditional foetal stethoscope and are found commonly in the labour rooms and the antenatal clinics.