Case report

The Ductus Venosus (DV) is a thin hourglass-shaped vessel (2cm long - 2mm wide) that connects the Umbilical Vein (UV) (4 times the size of the DV) to the heart. It arises from the Portal Sinus at the site of termination of the UV and joins with the IVC just before it enters the Right Atrium.

The DV allows the highly oxygenated blood (approximately 80% O2 saturation) from the placenta, through the UV, to bypass the liver and join the left heart through the Foramen Ovale. In animals, 50% of the UV blood flow is diverted to the left heart via the DV. In the human fetus, however, the Doppler ultrasound approach has suggested that this amount could be reduced to 20-30%.

The DV does not mix blood with the IVC (as it occupies the anterior part of the IVC). Its anatomic size and orientation is such that the oxygen-rich blood within the DV is accelerated (60-85 cm/s in the second part of gestation) and directed straight across the FO and into the Left Atrium. Highly oxygenated blood from the placenta and UV is thus directed into the Left Atrium, Ventricle and Ascending Aorta, bringing high oxygen content to the coronary and cerebral circulations.

The DV can be visualized in an axial plane of the upper abdomen. From the axial plane at the level of the abdominal circumference, the DV is seen as a narrow vessel arising from the UV. The DV can also be imaged in a mid sagittal longitudinal view of the abdomen (preferred view in early gestation) where the junction between the DV and the UV is seen and the narrow size of the DV is appreciated. The visualization of the DV is facilitated by the use of color Doppler, which reveals the presence of color aliasing, a feature that helps in the identification of the DV

The Doppler waveform of the DV is triphasic in morphology with a first peak concomitant with systole (S); a second peak concomitant with early diastole (passive filling of the ventricles (D)); and a nadir concomitant with the atrial (kick) contraction (A). Unlike the IVC and Hepatic Veins (HV), forward flow is present throughout the entire cardiac cycle in the DV, in the normal fetus.

Abnormal findings in the DV Doppler waveforms occur in the presence of severe intrauterine growth restriction and involve reduced, absent or reversed flow in the atrial contraction portion of the waveform. Abnormal DV waveforms can also be seen in obstructive lesions of the right heart.