Abstract
Critical fetal organs are preferentially supplied with oxygenated blood from the umbilical vein (UV) by way of the ductus venosus (DV). Under normal conditions a significant part of UV-blood flows steadily forward through the left portal vein (LPV). Blood flow through the LPV could reverse, however, in cases of absent or reversed endodiastolic flow in the umbilical arteries. We tested when fetal blood flow reversal occurs by studying 28 cases with pathological flow in the umbilical artery. In the LPV we observed normal nonpulsatile forward flow in 9 cases, pulsatile forward flow in 10 cases, and reversed flow in 9 cases. Reverse flow in the LPV correlated significantly with an elevated resistance index of the umbilical arteries. This reversal could have major physiological implications: Deoxygenated blood may be added via the LPV to the blood shifted through the DV and ultimately reach critical fetal organs. In extremis there could be a waterhose effect, whereby more blood flows through the DV than the UV that supplies it. The LPV is thus the watershed of the venous circulation of the fetus.
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