Relationship between placental blood flow resistance and precordial venous Doppler indices.

Abstract

To characterize the relationship between placental blood flow resistance and precordial venous Doppler indices in normal fetuses. This was a prospective cross-sectional Doppler study of uncomplicated pregnancies. Umbilical artery (UA), inferior vena cava (IVC) and ductus venosus (DV) were examined. Multiple indices were calculated for each vein and correlated with the UA pulsatility index (PI) and gestational age (GA). In addition, an arteriovenous ratio (AV ratio) between the UA PI and multiple venous indices was calculated and related to GA. In the 237 patients studied all venous indices showed a linear relationship with the UA PI. All venous indices except the IVC preload index (PLI) had a significant positive correlation with the UA PI. Seven AV ratios were calculated and each had a linear negative relationship with GA. The relationship between UA PI and IVC pulsatility index for veins (PIV) and DV PIV remained constant throughout gestation. The AV ratio that utilized the IVC PLI and DV systolic/a-wave ratio showed a significant decline with GA. Placental blood flow resistance least influences the IVC PLI while the converse is true for the PIV in both veins. A differential effect of placental afterload on various venous indices needs to be accounted for in situations of elevated placental blood flow resistance. AV Doppler ratios may be useful for this purpose.