title: Effects of different sampling points on evaluation of fetal descending aortic flow.
abstract: BACKGROUND
  Widespread use of fetal aortic blood flow velocity measurements for assessment of fetal circulatory status has been precluded by difficulties in achieving an adequate Doppler insonation angle at particular sampling points. The goal of this study was to evaluate the differences in resistance index (RI) and systolic peak velocity (Vmax) of fetal aortic blood flow velocity waveforms throughout gestation among various Doppler sampling points.
  
  
  METHODS
  A total of 551 normal women between 18-41 weeks of pregnancy participated in this study. Pulsed Doppler flow velocity waveforms were acquired from three different aortic sampling points (thoracic portion, beneath the diaphragm, and abdominal portion) of the fetal descending aorta. The Vmax and RI were calculated at the respective sampling points.
  
  
  RESULTS
  The Vmax were significantly lower in abdominal portion than those in thoracic portion at every time point (from 69 +/- 11 cm/second in thoracic to 49 +/- 8 cm/second in abdominal portion at 18-19 gestational weeks, p<0.0001), and RI were also lower (from 0.84 +/- 0.05 in thoracic portion to 0.76 +/- 0.05 in abdominal portion at 18-19 gestational weeks, p<0.0001). Significant increase in the Vmax was seen until third trimester (from 58+/-10 cm/second at 18-19 gestational weeks to 113 +/- 13 cm/second at 38-39 gestational weeks beneath the diaphragm, p<0.0001), while the RI remained stable (0.79 +/- 0.04 at 18-19 gestational weeks; 0.80 +/- 0.05 at 38-39 gestational weeks beneath the diaphragm).
  
  
  CONCLUSIONS
  In measuring the fetal circulatory status, these data demonstrate that the sampling point should be considered when evaluating the maximum systolic velocity and the resistance index of the fetal descending aorta.
authors.affiliation: Department of Obstetrics and Gynecology, Osaka City University, Graduate School of Medicine, Japan. rika@med.osaka-cu.ac.jp
authors.forename: Rika
authors.initials: R
authors.lastname: Nishihara
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Nakai
authors.forename: Daisuke
authors.initials: D
authors.lastname: Tachibana
authors.forename: Sei-ichi
authors.initials: S
authors.lastname: Yamamasu
authors.forename: Naoko
authors.initials: N
authors.lastname: Iwanaga
authors.forename: Osamu
authors.initials: O
authors.lastname: Ishiko
mesh_terms: D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000196:embryology* / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D005333:Fetus / Q000098:blood supply*; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D012039:Regional Blood Flow / Q000502:physiology; D013599:Systole / Q000502:physiology; D018617:Ultrasonography, Doppler, Pulsed / Q000379:methods*; D016216:Ultrasonography, Prenatal / Q000379:methods; D014655:Vascular Resistance / Q000502:physiology