A prospective study of the umbilical artery waveform in appropriate-for-date and growth-retarded fetuses.

Blood velocity waveforms were obtained by a combination of real-time B-mode and pulsed Doppler (2 MHz) ultrasound from the umbilical artery. In a prospective study, velocity waveforms of the umbilical artery were analyzed from 36 patients with single pregnancies. Sonograms were performed every 2nd week from the 18th week menstrual age onwards till labor. A total of 331 velocity profiles were obtained. Reference values were obtained from 27 patients with uncomplicated pregnancies. Abnormal waveforms were found in 9 cases. A comparison was made between the normal and abnormal group with regard to placental impedance indices [resistance index (RI), A/B ratio and pulsatility index (PI)]. The sensitivity, specificity, predictive values of each mentioned index were determined. The sensitivity of the PI and the RI is the same: 77.8%, the sensitivity of the A/B ratio is 66.7%. The specificity is also slightly higher for the PI and RI than for the A/B ratio (81.5, 81.5 and 77.5%, respectively). The same can be said for the predictive values (predictive value with positive result, 58.3, 58.3 and 50.0%, predictive value with negative result, 91.2, 91.2 and 87.5%). On the basis of these results and theoretical considerations, the PI is preferable to the other two placental impedance indices. It was shown once more that, with certain restrictions, this noninvasive transcutaneous technique reflects fetal well-being.