Assessment of Fetal Compromise by Doppler Ultrasound Investigation of the Fetal Circulation: Arterial, Intracardiac, and Venous Blood Flow Velocity Studies

Abstract

Background Doppler studies of the fetal circulation in intrauterine growth retardation and hypoxia have demonstrated a compensatory redistribution of arterial blood flow with increased flow to the cerebrum and myocardium and decreased flow to the periphery. The aim of this study was to evaluate the significance of changes in fetal venous blood flow waveforms in high-risk pregnancies and to investigate the time relation between alterations in venous and arterial Doppler waveform indices in compromised fetuses. Methods and Results The cross-sectional study consisted of 108 high-risk singleton pregnancies between 23 and 42 weeks’ gestation without fetal chromosomal abnormalities or major malformations. Blood flow velocity waveforms were recorded from the umbilical arteries, descending thoracic aorta, middle cerebral artery, tricuspid and mitral ventricular inflow, ductus venosus, inferior vena cava, and the right hepatic vein. The mean velocity and pulsatility index were calculated for arterial vessels, the E/A ratio for atrioventricular blood flow, and peak forward velocities during ventricular systole and early diastole, the lowest forward velocity or peak reverse velocity during atrial contraction, and time-averaged maximum velocity for venous vessels. Two ratios for venous waveforms, one of which is the equivalent of the pulsatility index, were calculated. Fetal biophysical assessment was based on a computerized cardiotocogram and the biophysical profile score. The compromised group consisted of 37 fetuses delivered by cesarean section for an abnormal heart rate trace (n=21) or severe preeclampsia (n=9) or which died in utero (n=7) within 10 days of their last Doppler investigation. This group showed significant alterations in arterial and venous flow velocity waveforms but not in atrioventricular inflow. Additionally, to find out whether venous Doppler investigation may help to detect a worsening of the situation in fetuses already showing arterial blood flow redistribution, we analyzed the data of these fetuses separately. The 41 fetuses that had an aorta/middle cerebral artery pulsatility index ratio >95th percentile were divided into compromised and noncompromised groups according to their biophysical assessment and whether or not they developed fetal distress (cesarean section for abnormal heart rate trace or intrauterine death). The mean values for Doppler parameters of the compromised groups differed significantly from the noncompromised groups in all venous vessels, whereas differences on the arterial side were much less pronounced. Velocity ratios of venous waveforms were significantly higher, and absent or reverse flow in the ductus venosus with atrial contraction indicated a poor prognosis, with a perinatal mortality of 5 out of 8. Conclusions Fetal compromise is associated with significant alterations in the fetal arterial and venous circulation. Significant changes in venous Doppler waveforms develop due to increased afterload and perhaps myocardial failure in late deterioration after fetal arterial redistribution is established and seem to be closely related to abnormal biophysical assessment findings. Therefore, Doppler investigation of the fetal venous circulation may play an important role in monitoring the redistributing growth retarded fetus and thereby may help to determine the optimal time for delivery.