title: Relationship between placental blood flow resistance and precordial venous Doppler indices.
abstract: OBJECTIVE
  To characterize the relationship between placental blood flow resistance and precordial venous Doppler indices in normal fetuses.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Sciences, University of Maryland, Baltimore, MD 21201-1703, USA. abaschat@umm.edu
authors.forename: A A
authors.initials: AA
authors.lastname: Baschat
mesh_terms: D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D008099:Liver / Q000098:blood supply; D021041:Placental Circulation / Q000502:physiology*; D011247:Pregnancy; D011446:Prospective Studies; D011673:Pulsatile Flow / Q000502:physiology; D018608:Ultrasonography, Doppler / Q000379:methods; D016216:Ultrasonography, Prenatal / Q000379:methods*; D014469:Umbilical Arteries / Q000000981:diagnostic imaging / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology*; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging / Q000502:physiology