An Instrument for Recording the Fetal Pulse Rate

An instrument is described for recording the fetal heart rate using a microphone strapped onto the abdomen. Special precautions have been taken to reduce the effects of extraneous noise received by the microphone. The electronic system incorporates a narrow passband amplifier, a rapidly responding automatic gain control circuit, and a ratemeter in which the intervals between successive pulses are compared so that pulses which are unlikely to be genuine can be disregarded. The equipment is suitable for operation by nontechnical personnel, and has been used regularly in a maternity hospital for a period of eighteen months.