Measurement of Systolic-Diastolic Ratio in the Umbilical Artery by Continuous-Wave and Pulsed-Wave Doppler Ultrasound: Comparison at Different Sites

Abstract

Analysis of umbilical artery flow velocity waveforms, especially systolic-diastolic (S-D) ratio, can predict some pregnancy abnormalities. Most of the earlier studies did not specify the exact segment of umbilical artery sampled. We studied 53 normal singleton pregnancies between 18-41 weeks' gestation to compare S-D ratio measurements of the umbilical artery at different sites: 1) abdominal insertion site, 2) placental insertion site, 3) mid-cord, and 4) an undetermined site. The mean S-D ratio was significantly different (P less than .01) at various segments of the umbilical artery--higher near the abdominal insertion site when compared with the mid-cord, near-placental, and undetermined sites. The S-D ratio at mid-cord was higher than at the undetermined site and the placental insertion site. The near-placental-site S-D ratio was not different from the undetermined site. A lower S-D ratio at the undetermined site may not adequately reflect the true physiologic status of the fetus. Specifying the site of measurement should be an integral part of any report, in order to describe accurately the pathophysiology of fetoplacental circulatory diseases.