The fetal central venous pressure waveform in normal pregnancy and in umbilical placental insufficiency

OBJECTIVE: Our purpose was to study the fetal central venous pressure waveform recorded noninvasively from the inferior vena cavea in normal and complicated pregnancies by means of newly developed equipment to follow the vessel lumen diameter. STUDY DESIGN: A paired ultrasonic phase-locked loop echo tracking system with a high sampling frequency (3000 Hz) was used to follow the movement (point displacement) of diametrically opposite points of the vessel wall. The lumen was measured as the interval between these points. We studied 70 normal fetuses (20 to 40 weeks) and 54 complicated pregnancies with increased umbilical placental resistance. RESULTS: The four component waves of the central venous pressure waveform (A, X, V, Y) were identified and measured in the fetal recording. The crests of the A and V waves were of approximately equal height. An increase in the descent of the Y trough was observed with advancing gestation. By means of data from the normal group, the complicated group was divided into three subgroups. In 10 fetuses the waveform was normal. In 31 there was a high pulsatile pattern with deep descent from the A crest to X trough so that the pulsatility of the waveform appeared increased. In 13 this was shallow and the pulsatility appeared reduced. Clinical outcome (nonreactive fetal heart rate, percentile birth weight, days in neonatal intensive care unit) was significantly worse in both these latter two subgroups in comparison with normal and in the low compared with the high-pulsatile group. CONCLUSIONS: Human fetal central venous pressure waveforms can be simply recorded and represented by the transluminal diameter waveform. In fetal compromise the high pulsatility waveform may result from a reduced ventricular ejection and increased end-diastolic pressure in response to the increase in ventricular afterload caused by the placental vessel obliteration. In the most profoundly compromised fetuses the low pulsatility waveform may indicate depressed myocardial function and output.