RELIABILITY OF ULTRASOUND AS COMPARED TO DIRECT FETAL ELECTROCARDIOGRAPHY FOR ANTEPARTUM CARDIOTOCOGRAPHY

Abstract

Eighty-five pairs of simultaneously recorded external and internal cardiotocograms (CTGs) were coded and evaluated with a ten-point scoring system routinely used for the assessment of antepartum CTG. The highest consistency in interpretation between the external ultrasound and the internal fetal scalp CTG was found for basal heart rate followed by decelerations. Oscillatory amplitude and frequency were interpreted differently in 14 per cent of CTGs and accelerations in 16 per cent. When differences in interpretation arose, there was certainly no tendency for the external CTG to present an optimistic image of the fetal heart rate variables. With the exception of oscillatory amplitude all variables, including oscillatory frequency and the total CTG score, were more frequently underestimated than overestimated on external CTGs. When accelerations were present on only one recording, there was an 85 per cent chance for these to be absent on the external CTG. The study abolishes fears that the routine clinical assessment of antepartum CTGs of adequate technical quality provides overrated and more optimistic data than would by achieved by direct fetal scalp monitoring.