Objective: To determine the degree of ductus venosus (DV) shunting in fetuses with intrauterine growth restriction (IUGR) and the effect of various degrees of umbilical circulatory compromise.
Methods: This was a cross-sectional observational study. Sixty-four fetuses with IUGR (estimated weight < or = 2.5(th) percentile) underwent ultrasound examination. The diameter, velocity, and blood flow were determined in the DV and intra-abdominal umbilical vein (UV), and the fraction of shunting and DV : UV diameter ratios were calculated. Placental compromise was classified according to either normal umbilical artery (UA) pulsatility index (PI), UA-PI > 97.5(th) percentile, or absent or reversed end-diastolic flow velocity (A/REDV). Regression analysis was used to construct mean values, and SD scores were used to determine differences compared with a reference population (n = 212) after ln- or power-transformation.
Results: In the 64 growth-restricted fetuses, the average DV shunting was 39% compared with 25% in the reference group (overall P < 0.0001). The corresponding values in the subgroups with normal UA-PI, UA-PI > 97.5(th) percentile, and A/REDV were 31%, 35%, and 57%, respectively. Fetuses with IUGR and normal UA-PI (SD score: mean, 0.48; 95% CI, 0.04-0.92) did not shunt significantly more than did the reference fetuses (SD score: mean, 0.0; 95% CI, - 0.15 to 0.15), but those with UA-PI > 97.5(th) percentile (SD score: mean, 0.85; 95% CI, 0.41-1.29), and particularly those with A/REDV (SD score: mean, 1.56; 95% CI, 1.0-2.12) did shunt significantly more. With more DV shunting, these fetuses distributed correspondingly less umbilical blood to the liver, one of the mechanisms being a lower perfusion pressure as reflected in the lower DV blood velocity (P < 0.0001).
Conclusions: DV shunting is higher and the umbilical blood flow to the liver is less in fetuses with IUGR, particularly in those with the most severe umbilical hemodynamic compromise.