ABDOMINAL VENOUS SYSTEM IN THE NORMAL FETUS

Objective: To assess flow velocity waveforms of the abdominal venous system in the normal fetus. Methods: Sixty-seven normal fetuses between 17-42 weeks' gestation were each studied once. Flow velocity waveforms were obtained from the following: 1) umbilical vein at the entrance into the abdomen, 2) umbilical sinus, 3) portal vein before its division, 4) anterior division of the portal vein, 5) posterior division of the portal vein, 6) ductus venosus at its origin from the umbilical vein, 7) splenic vein at its origin, 8) splenic vein close to the umbilical sinus, 9) renal vein, 10) adrenal vein, 11) common iliac vein before the origin of the inferior vena cava, 12) inferior vena cava, and 13) left hepatic vein. Results: Five different patterns were noted on the velocity waveforms of the abdominal venous system: continuous, monophasic, biphasic, triphasic, and tetraphasic. Conclusion: In the normal fetus, all veins leading to the liver have continuous now, except the umbilical sinus, which has a monophasic pattern. The ductus venosus has a biphasic pattern. The veins that open into the inferior vena cava have triphasic now velocity waveforms. The left hepatic vein occasionally has a tetraphasic pattern.