Components of variability of umbilical arterial Doppler velocimetry--a prospective analysis

This study prospectively analyzed the components of variance and error contributions of umbilical arterial Doppler indices in a normal pregnant population (308 women) with gestational ages ranging from 27 to 40 weeks. A continuous-wave Doppler instrument with a 4 MHz transducer was used. The Doppler indices measured were systolic/diastolic ratio, diastolic/average ratio, pulsatility index, and resistance index. The contributions of gestational age, fetal heart rate, location of measurement, interobserver variability, and intraobserver variability on the variance were studied. The investigation demonstrated that the gestational age and fetal heart rate contributed to 33% to 46% and 15% to 18% of the variance, respectively. The location of the Doppler measurement contributed to 29% to 46% of the error variance. Additionally, the interobserver and intraobserver error variance amounted to 10% to 14% and 5% to 9%, respectively. Of these various factors, the interobserver and intraobserver variance were related to the nonhemodynamic phenomena and therefore represented error components. It is obvious that these factors that affect the variance of the Doppler indices should be considered before the diagnostic reliability of this technique can be critically evaluated.