ABDOMINAL VENOUS SYSTEM IN THE NORMAL FETUS

Objective: To assess flow velocity waveforms of the abdominal venous s ystem in the normal fetus. Methods: Sixty-seven normal fetuses between 17-42 weeks' gestation were each studied once. Flow velocity waveform s were obtained from the following: 1) umbilical vein at the entrance into the abdomen, 2) umbilical sinus, 3) portal vein before its divisi on, 4) anterior division of the portal vein, 5) posterior division of the portal vein, 6) ductus venosus at its origin from the umbilical ve in, 7) splenic vein at its origin, 8) splenic vein close to the umbili cal sinus, 9) renal vein, 10) adrenal vein, 11) common iliac vein befo re the origin of the inferior vena cava, 12) inferior vena cava, and 1 3) left hepatic vein.Results: Five different patterns were noted on th e velocity waveforms of the abdominal venous system: continuous, monop hasic, 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 h as a biphasic pattern. The veins that open into the inferior vena cava have triphasic now velocity waveforms. The left hepatic vein occasion ally has a tetraphasic pattern.