Reference values of fetal aortic flow velocity waveforms and associated intra-observer reliability in normal pregnancies.
OBJECTIVE
It was the aim of the present study to calculate new Doppler reference ranges for blood flow velocities (Vmax, Vmean, Vmin) and resistance indices (PI, RI) for the fetal descending aorta by automatic waveform analysis.


METHODS
Cross-sectional prospective study.


METHODS
Nine hundred and twenty-six low-risk pregnancies at 18-41 weeks' gestation.


METHODS
Aortic blood flow velocities were derived with pulsed-wave color Doppler. Measurements were carried out at the level of the diaphragm. Reference ranges for the individual measuring parameters were constructed based on a growth function from a four-parameter class of monotonic continuous functions according to the smallest square principle. Further investigated were intra-observer reliability and the influence exerted by different measuring sites (aortic arch, diaphragm, below the renal vessels) on the aortic Doppler flow spectrum.


RESULTS
Although a significant increase in aortic blood flow velocity was observed at 18-41 weeks' gestation (Vmax = 48.2 cm/s to 110.3 cm/s (P < 0.001), Vmean = 20 cm/s to 47.5 cm/s (P < 0.001) and Vmin = 7.6 cm/s to 18.6 cm/s (P < 0.001)), there were no significant changes in the pulsatility or resistance indices. The resistance indices PI and RI as well as absolute blood flow velocities (Vmax, Vmin) were significantly lower with increasing distance from the heart. Initial decreases were measured between the aortic arch and the diaphragm: PI, 2.34 to 1.87 (P < 0.0001); RI, 0.87 to 0.79 (P < 0.0001); Vmin: 8.5 cm/s to 15.0 cm/s (P < 0.0001). Furthermore, systolic blood flow velocities (Vmax) were decreased below the renal vessels from 97 cm/s to 64 cm/s (P < 0.0007). No significant changes were recorded in intensity-weighted mean flow velocities (Vmean). The intra-observer reliability was low, but of no clinical relevance.


CONCLUSIONS
At constant measuring conditions, the reference ranges for blood flow velocities and resistance indices in the fetal aorta calculated by the authors serve as the basis for Doppler ultrasound antenatal examinations in a normal patient population and enable the early diagnosis of fetal risk.
Department of Obstetrics and Gynecology, University of Mainz, Mainz. bahlmann@mail.uni-mainz.de
F
F
Bahlmann
S
S
Wellek
I
I
Reinhardt
F
F
Krummenauer
E
E
Merz
C
C
Welter
D001013:Aorta, Thoracic / Q000000981:diagnostic imaging* / Q000196:embryology; D001783:Blood Flow Velocity; D003430:Cross-Sectional Studies; D005260:Female; D005333:Fetus / Q000098:blood supply*; D005865:Gestational Age; D006801:Humans; D015588:Observer Variation; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D018615:Ultrasonography, Doppler, Color; D016216:Ultrasonography, Prenatal