The measurement of fetal systolic time intervals: lessons from ultrasound

Fetal systolic time intervals (pre-ejection period, iso-volumetric contraction time and ventricular ejection time) can be measured using Doppler ultrasound to detect valve movements and the fetal ECG to indicate the onset of ventricular depolarisation. Continuous recordings of FSTI, fetal heart rate and uterine activity depict changes reflecting progressive cord compression and have the potential for providing improved differentiation of late and variable decelerations. However, the continual adjustment of the ultrasound transducer required to maintain a good signal limits the technique. Recent improvements in phono indicate that this may provide a useful alternative, provided that suitable signal-processing is developed.