[Studies on the cardiotocograms recorded by a new system with 1 MHz ultrasound and autocorrelation heart rate meter]

Improved FHR records were obtained by the use of a new 1 MHz ultrasound transducer and autocorrelation heart rate meter. The results were compared with conventional 2.5 MHz continuous wave ultrasound device. The rate of the loss of FHR recording was 0 to 6.6% (2.8 +/- 2.1%) in the new device, and it was 2.1 to 23.5% (8.7 +/- 6.2%) in the old one. The loss of FHR record in the 2nd stage of labor was 3.2% when 1 MHz ultrasound and new device were used, and it was 2.0% with direct fetal ECG signal using scalp electrode and the same device. More clear record was obtained with use of ultrasound at a crowning of fetal head than that of direct fetal ECG. In the use of 1 MHz ultrasound, 51% cases in 55 patients showed undisturbed FHR record 1 minute before delivery of the fetus. Slightly noisy but analysable FHR record was obtained in 36%. Hence, the FHR records were clearly evaluated until 1 minute before delivery of the infant in 87% of the cases. Maternal heart rate signal was mixed with FHR in 2 cases in routine intrapartum ultrasonic FHR monitoring. However, the maternal signal disappeared after moving the transducer to other position where fatal heart beat was more clearly detected.