An Inductive Sensor For Recording Of Fetal Movements And Sounds

In this paper we present a transducer based on an inductive principle which enables recording of fetal movement signals on the maternal abdominal wall. The transducer is a relatively passive device in contrast to commonly applied ultrasound transducers. This enables long-term observation of fetal movements and sounds. The bandwidth of the system is DC - 200 Hz. The transducer has been applied to study fetal respiratory sinus arrhythmia. Therefore fetal breathing movements have to be extracted from the transducer's output. This proved possible by digitally filtering of the displacement signal as detected by the transducer. The transducer has also been applied in a study where the signal-to-noise ratio of fetal heart sounds as function of location of the fetus and position of the transducer on the maternal abdominal wall has been studied. It proved possible to adequately record fetal heart sounds for measurement of fetal heart rate. Uterine activity could be recorded using the sensor's DC-output.