In a comparative study on 484 pregnant women the influence of different modifications of the examination by continuous wave (cw)--Doppler was tested. The aim was to improve the detection rate of foetal growth retardation (IUGR): 1. Among different definitions of normal ranges the mathematical "smoothing" of normal values by regression analysis improves the results. 2. Of the most commonly used flow indices the A/B ratio is more reliable than the resistance and the pulsatility index. 3. Comparing the results of one to three examinations of the same patient in the course of pregnancy the relation of sensitivity to specificity is best after two examinations. 4. On evaluating the examinations of the umbilical arteries and the arcuate arteries, an intolerably false positive rate was found in the evaluation of arcuate arteries by cw Doppler.