Umbilical artery half peak systolic velocity deceleration time throughout pregnancy and its role in fetuses with bradycardia

摘要

Objectives To describe a new technique for Dopplerwaveform quantification of the fetal umbilical artery,the half peak systolic velocity (h-PSV) deceleration time,which measures the time that it takes a single flow velocitywaveform to halve its maximum systolic velocity. As thismeasurement is independent of fetal heart rate, its role inthe evaluation of placental vascular resistance in fetuseswith bradycardia was also explored.Methods The umbilical artery impedance indices and theh-PSV deceleration time were measured in 532 normalsingleton fetuses from 17 to 41 weeks of gestation. Anomogram was established and its usefulness in assessingfetuses with bradycardia was evaluated.Results The relationship between umbilical artery h-PSVdeceleration time and gestational age was best describedby a linear formula (y = 6.5523x + 12.41; R2 = 0.6346),h-PSV deceleration time increasing by 6.6 ms per week.The correlation coefficients for the 95th, 50th and 5thcentiles were 0.97, 0.98 and 0.98, respectively. Measurementof h-PSV deceleration time was reproducible, withinterobserver and intraobserver variabilities of 10.7%and 7.4%, respectively. Among fetuses with bradycardia(n = 7), the h-PSV deceleration time was above the 5thcentile in all cases, suggesting normal placental function inspite of abnormally increased impedance indices obtainedwith traditional Doppler indices in six.Conclusions The h-PSV deceleration time increaseslinearly during the second and third trimesters ofpregnancy. As its measurement is reproducible andindependent of heart rate, it may be useful in the assessment of well-being in fetuses with bradycardia.