Intra‐observer and inter‐observer reliability of the pulsatility index calculated from pulsed Doppler flow velocity waveforms in three fetal vessels

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Abstract
Objective Study of the intra observer and inter observer reliability of the pulsatility index, calculated from pulsed Doppler recordings of three fetal vessels.Design Flow velocity waveforms (FVW) were recorded from the umbilical artery, the fetal descending aorta and the fetal internal carotid artery. Intra‐observer reliability was assessed in six fetuses; ten repeated measurements were performed by one observer. Inter‐observer reliability was studied in 14 fetuses; two observers performed two repeated measurements in each fetus.Setting A tertiary referral hospital.Subjects High risk pregnancies with a gestational age ranging from 29 to 42 weeks.Main outcome measures Analysis of variance with repeated measurements and a graphical method were used for data analysis. Intra‐observer repeatability was expressed as Intraclass Correlation Coefficient (IntraCC). Inter‐observer agreement was expressed as Interclass Correlation Coefficient (InterCC).Results IntraCC for umbilical artery, descending aorta and internal carotid artery were 0.91, 0.78, and 0.54, respectively. InterCC values for these vessels were 0.39, 0.45 and 0.34, respectively. No systematic differences between the two observers except for the fetal descending aorta, were apparent. IntraCC decreased remarkable when fetuses with absent end diastolic velocities were excluded from the analysis.Conclusion The pulsatility index (PI) used for fetal measurements has a poor reliability. This is of serious concern when clinical use of FVW measurements is considered as a diagnostic tool.