[Doppler evaluation of the fetal arterial circulation: reference values of the Resistance Index and Pulsatility Index between the 28th and 41st weeks of gestation].

The authors established reference ranges for the Resistance Index and the Pulsatility Index of the umbilical artery, the fetal descending aorta and the middle cerebral artery in order to facilitate the uniform evaluation of the Doppler ultrasound examination in obstetrics. 164 patients with uncomplicated pregnancies between the 28th and 41st weeks of gestation were recruited for the longitudinal assessment of Doppler Resistance Indices and Pulsatility Indices in the fetal and umbilical arteries. Data were retrospectively analysed in order to establish the weekly mean values and standard deviations. The mean values of the indices in three periods (I.: 28-31, II.: 32-36, III.: 37-41 weeks) were compared. The normal haemodynamic resistance is reflected by the Doppler indices within the weekly mean +/- 2SD range. The results designate decreasing haemodynamic impedance in the umbilical and in the middle cerebral arteries while the resistance to the blood flow in the abdominal aorta is constant throughout the third trimester of gestation. The introduction and the clinical application of the reference values provides appropriate interpretation of the physiologic fetal blood flow patterns which is the prerequisite of the diagnostic accuracy of the Doppler ultrasound in obstetrics.