The umbilical artery Doppler ultrasonographic gradient: confirmation, cause, and comparison of continuous-wave and duplex ultrasonographic pulsed-wave measurements.

The umbilical artery Doppler ultrasonographic gradient has been described, and the need for site-specific nomograms has been pointed out. However, controversy still exists about the cause of this phenomenon and the optimal site for obtaining umbilical artery Doppler ultrasonographic measurements. Cross-sectional measurements of umbilical artery flow velocity waveform (FVW) systolic/diastolic (S/D) ratios were therefore made in 35 gravid women during the second or third trimester of pregnancy with both duplex pulsed-wave (PW) and free-standing continuous-wave (CW) Doppler ultrasonographic equipment. Multiple duplex PW Doppler ultrasonographic signals were recorded at the abdominal cord insertion, placental cord insertion, and free cord sites. Multiple CW Doppler FVWs were obtained from four quadrants, in decreasing order of ease of measurement. Repeated-measures analysis of variance demonstrated a statistically significant decrease in mean and median values of the umbilical artery S/D ratio from the abdominal cord insertion site to the placental cord insertion site. The reduction in the value of the S/D ratio as the placental cord insertion site is approached results more from a decrease in the peak systolic maximum velocity envelope than from an increase in diastolic velocities. Moreover, mean and median CW Doppler ultrasonographic values correlate most closely with corresponding PW measurements of the free cord segment. These data confirm the presence of the umbilical artery Doppler ultrasonographic gradient. Decreasing values of the S/D ratio from the fetal abdomen to the placenta are a result of attenuation of the systolic maximum velocity envelope.(ABSTRACT TRUNCATED AT 250 WORDS)