Objective: The purpose of this study was to evaluate the changes in the distribution of the umbilical venous blood flow to the liver and to the ductus venosus in intrauterine growth-restricted human fetuses in relationship with dilation of the ductal isthmic diameter.
Study design: Umbilical venous flow, ductus venosus blood flow, and blood flow to the fetal liver were measured in 56 severely intrauterine growth-restricted fetuses with an abnormal pulsatility index of the umbilical artery and were compared with 137 normal control fetuses. Percentages of umbilical venous blood flow through the ductus venosus and to the fetal hepatic lobes were calculated. Z-scores for control fetuses and intrauterine growth-restricted fetuses were constructed by the evaluation of the inverted smoothed percentiles. The distributions of the Z-scores was compared with a 1-sample t-test.
Results: The ductus venosus blood flow that was corrected for fetal weight was increased significantly in intrauterine growth-restricted fetuses compared with control fetuses (P=0); the median values (interquartile range) for comparable ages of gestation was 41.3 mL/min/kg (range, 26.2-64.0 mL/min/kg) and 30.8 mL/min/kg (range, 19.9-42.8 mL/min/kg), respectively. As a consequence, ductus venosus shunting was increased in intrauterine growth-restricted fetuses compared with control fetuses (P =0). In 23 of 30 intrauterine growth-restricted fetuses, the percentage of umbilical blood flow that was shunted through the ductus was>90th percentile of control fetuses. Ductal diameters were significantly greater in growth-restricted fetuses than in control fetuses (P =.0001). The percentage of blood flow to the right lobe showed a significant reduction (P =.0223), with evidence of reversed blood flow from the right lobe and portal system into the ductus venosus that was provided both by volume blood flow calculations and by direct pulsed Doppler waveform direction.
Conclusion: In severe intrauterine growth-restricted fetuses, Doppler examination of blood flow volume proved a significant increase in the shunting of umbilical vein blood flow through the ductus venosus that was associated with the dilation of the ductal isthmic diameter. These changes provide a relatively constant blood flow to the heart and brain at the expense of fetal hepatic perfusion.