Doppler waveforms from the uteroplacental and umbilical arteries were studied in 543 unselected women attending an antenatal clinic. Overall, 357 women were studied at 26-30 weeks and 395 at 34-36 weeks; 209 were studied at both gestation periods. Results were not made available to clinicians. There was no difference in outcome of pregnancies between those with normal and abnormal uteroplacental waveforms, but birthweights were significantly lower in those with an abnormal umbilical artery waveform at either gestation. There were no other statistically significant differences between groups. Although the power of the study to detect differences in outcome in this sample size is limited, our findings do not support the introduction of this new technique into clinical practice before sufficiently large randomized controlled trials have shown some benefit.