THE FETAL CENTRAL VENOUS-PRESSURE WAVE-FORM 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 cava in normal and complicated pregnancies by means of newly developed equipment to f ollow the vessel lumen diameter. STUDY DESIGN: A paired ultrasonic pha se-locked loop echo tracking system with a high sampling frequency (30 00 Hz) was used to follow the movement (point displacement) of diametr ically opposite points of the vessel wall. The lumen was measured as t he interval between these points. We studied 70 normal fetuses (20 to 40 weeks) and 54 complicated pregnancies with increased umbilical plac ental resistance. RESULTS: The four component waves of the central ven ous pressure waveform (A, X, V, Y) were identified and measured in the fetal recording. The crests of the A and V waves were of approximatel y equal height. An increase in the descent of the Y trough was observe d with advancing gestation. By means of data from the normal group, th e complicated group was divided into three subgroups. In 10 fetuses th e waveform was normal. In 31 there was a high pulsatile pattern with d eep descent from the A crest to X trough so that the pulsatility of th e waveform appeared increased. In 13 this was shallow and the pulsatil ity appeared reduced. Clinical outcome (nonreactive fetal heart rate, percentile birth weight, days in neonatal intensive care unit) was sig nificantly worse in both these latter two subgroups in comparison with normal and in the low compared with the high-pulsatile group. CONCLUS IONS: Human fetal central venous pressure waveforms can be simply reco rded and represented by the transluminal diameter waveform. In fetal c ompromise the high pulsatility waveform may result from a reduced vent ricular ejection and increased end-diastolic pressure in response to t he increase in ventricular afterload caused by the placental vessel ob literation. In the most profoundly compromised fetuses the low pulsati lity waveform may indicate depressed myocardial function and output.