A comparative clinical study of fetal phono- and movement-sensors from Amsterdam, Cambridge and Edinburgh

In a European collaboration, a joint project to conduct an experimental and clinical investigation of recently developed sensors from three centres (Amsterdam, Cambridge and Edinburgh) has been carried out. The Amsterdam sensor was based on an inductive principle whereas the Cambridge and Edinburgh transducers used a piezo-electric material (PVDF) as transducing element. Nine patients with varying gestational age (29-38 weeks) were measured in a clinical investigation. Recordings of fetal heart sounds (FHS) and fetal breathing movements (FBM) were made using three sensors; one from each centre. These recordings were digitized directly into a computer using a purpose-built data acquisition system. For each patient 3 min of FBM data, and 1 min of FHS data were recorded by each sensor. The FBM recordings were carried out simultaneously with ultrasound, so as to enable a correlation to be made between both recordings. The FHS recordings were carried out simultaneously with the maternal heart pulse, to discount any maternal heart influences on the resulting signals. Of the nine patients analysed, FHS were recorded in seven patients. On the other hand, it appeared difficult to identify fetal breathing movements in the FBM recordings due to the dominance of the maternal breathing component. The analysis of the FBM signals and its correlation with ultrasound could not be carried out due to the relatively poor quality of the signals detected by the sensors, given the present techniques of analysis. The evaluation of the FHS recordings showed that although there is relatively little difference between the sensors, the inductive sensor performed best.