Comparison between color Doppler cineloop- and conventional spectral Doppler-derived maximum velocity and flow in the umbilical vein

Abstract

Objective: To compare the umbilical venous flow velocity derived from color Doppler cineloop recordings with that derived from conventional spectral Doppler in normal pregnancies.

Method: In 18 uncomplicated pregnancies between 19 and 39 weeks' gestation, color Doppler was used to find the maximum velocity in the cross-sectional vessel area of a free-floating loop of the umbilical vein. The maximum velocity was determined using the software tool HDI_Lab (Philips Medical Systems) after tracing the vessel area of interest. Conventional spectral Doppler was then used to determine the maximum velocity with the High-Q machine option. The cross-sectional area of the umbilical vein was determined using B-mode imaging and was subsequently used to determine the umbilical volume flow from both Doppler methods. Assuming a parabolic flow profile in the umbilical vein, the mean velocity is equal to half the maximum velocity. The fetal weight was estimated from fetal biometry using the four-parameter Hadlock formula.

Results: Maximum velocity was significantly (P = 0.003) higher with color Doppler cineloop (14.3 +/- 2.5 cm/s) compared with spectral Doppler (12.7 +/- 3.2 cm/s). Therefore, using the same cross-sectional area for both methods, the umbilical blood flow was significantly higher (P = 0.001) with color Doppler cineloop (127.9 +/- 59.0 mL/min) than it was with spectral Doppler (112.8 +/- 54.1 mL/min). The umbilical blood flow expressed as volume flow per kg fetal weight was significantly (P = 0.01) higher with color Doppler cineloop (126.0 +/- 57.0 mL/min/kg) than it was with spectral Doppler (115.0 +/- 53.0 mL/min/kg).

Conclusions: Umbilical venous flow velocity derived from color Doppler cineloops is approximately 10% higher than that derived from spectral Doppler-derived velocity. The reduced angle dependence of the color Doppler cineloop technique and the large sampling area of the cross-sectional vessel should allow better determination of the correct maximum velocity in the umbilical vein.