BACKGROUND Abnormal waveforms from Doppler ultrasound may indicate poor fetal prognosis. It is also possible that Doppler ultrasound could encourage inappropriate early delivery. OBJECTIVES The objective of this review was to assess the effects of Doppler ultrasound in high risk pregnancies on obstetric care and fetal outcomes. SEARCH STRATEGY We searched the Cochrane Pregnancy and Childbirth Group trials register. SELECTION CRITERIA Randomised trials of Doppler ultrasound for the investigation of umbilical artery waveforms in high risk pregnancies compared to no Doppler ultrasound. DATA COLLECTION AND ANALYSIS Trial quality was assessed and data were extracted by both reviewers. Study authors were contacted for additional information. MAIN RESULTS Eleven studies involving nearly 7000 women were included. The trials were generally of good quality. Compared to no Doppler ultrasound, Doppler ultrasound in high risk pregnancy (especially those complicated by hypertension or presumed impaired fetal growth) was associated with a trend to a reduction in perinatal deaths (odds ratio 0.71, 95% confidence interval 0.50 to 1.01). The use of Doppler ultrasound was also associated with fewer inductions of labour (odds ratio 0.83, 95% confidence interval 0.74 to 0.93) and fewer admissions to hospital (odds ratio 0.56, 95% 0.43 to 0.72), without reports of adverse effects. No difference was found for fetal distress in labour (odds ratio 0.81, 95% confidence interval 0.59 to 1.13) or caesarean delivery (odds ratio 0.94, 95% 0.82 to 1.06). REVIEWER'S CONCLUSIONS The use of Doppler ultrasound in high risk pregnancies appears to improve a number of obstetric care outcomes and appears promising in helping to reducing perinatal deaths.