Variability of PI calculations.

In obstetrics the pulsatility index (PI) may be a useful parameter for the determination of fetal well-being. Although the PI is unambiguously defined, calculation from the measured data can be difficult. In order to study the comparability of PI values found by several investigators and with different methods tape recordings of Doppler signals of fetal vessels were used. The tapes were processed by several centres in Europe and the results were compared. Comparability is poor, although for the umbilical artery the results are in reasonable agreement. The method used has its drawbacks but shows that one must be careful in comparing results from different centres.