INTERMACHINE ERROR IN FETAL DOPPLER FLOW VELOCITY WAVE-FORM ANALYSIS - A PRELIMINARY-REPORT

Objective: The aim of the study was to establish inter-machine reproducibility of the pulsatility index and resistance index calculated from Doppler flow velocity waveforms from the fetal umbilical artery. Methods: Studies of fetal umbilical artery waveforms from two patients at 36 weeks' gestation were performed by a single operator. A Diasonics DRF 400 machine was paired with one of two Toshiba 270 machines and studies were alternated between machines during a session. Between 8 and 15 examinations were performed per machine per session. The mean of five consecutive waveforms was measured on line for each examination. Results: The pulsatility index from the same patient was significantly different between machines (session 1: 1.14 vs 0.78, P = 0.0013; session 2; 1.08 vs 0.72, P = 0.0009; session 3: 1.17 vs 1.00, P = .0001; session 4: 1.20 vs 0.86, P = 0.0003) but was not significantly different using either the Diasonics machine (1.14 vs 1.08 vs 1.17, P = 0.5949) or a Toshiba machine with different probes (0.78 vs 0.72, P = 0.4598) on the same patient at different sessions. The resistance index from the same patient did not differ between machines (0.66 vs 0.62, P = 0.2778; 0.64 vs 0.66, P = 0.3367). Conclusions: There may be large intermachine variations in the on-line calculation of the pulsatility index from the fetal umbilical artery. Caution is warranted when comparing the pulsatility index either between centers or from the same center when different equipment is used. Further studies are necessary to confirm that the resistance index is reproducible with different machines.