REFERENCE RANGES FOR FETAL VENOUS AND ATRIOVENTRICULAR BLOOD-FLOW PARAMETERS

This cross-sectional study establishes reference ranges with gestation for Doppler parameters of fetal venous and atrioventricular blood flo w. Color flow Doppler was used to examine 143 normal singleton pregnan cies at 20-40 weeks' gestation. Flow velocity waveforms were recorded from the ductus venosus, right hepatic vein and inferior vena cava. Th e waveforms are triphasic, reflecting ventricular systole, early diast ole and atrial contraction. Peak velocities for these parameters were measured with pulsed Doppler and a new index, the peak velocity index for veins (PVIV), was calculated. Similarly, time-averaged maximum vel ocities for the whole cardiac cycle were measured and the pulsatility index for veins (PIV) was calculated. Flow velocity waveforms were als o recorded at the level of the atrioventricular valves and the ratios of peak velocities at early diastolic filling (E) and atrial contracti on (A) were calculated. Regression analysis was used to define the ass ociation of each measured and calculated Doppler parameter with gestat ional age. Blood flow velocities in the fetal veins and velocities and E/A ratios across the atrioventricular valves increased significantly with gestation, whereas PVIV and PIV decreased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic ve in, and PVIV and PIV were highest in the hepatic vein and lowest in th e ductus venosus. In the ductus venosus, there was always forward flow throughout the heart cycle, whereas in the inferior vena cava and hep atic vein during atrial contraction, flow was away from or towards the heart or there was no flow. Pulsatility of flow velocity waveforms in the venous system is the consequence of changes in pressure differenc e between the venous system and the heart during the heart cycle. The finding that PVIV and PIV decrease with gestation is consistent with d ecreasing cardiac afterload and maturation of diastolic ventricular fu nction.