BACKGROUND Doppler ultrasound study of umbilical artery waveforms helps identify the compromised fetus in 'high risk' pregnancies and, therefore, deserves assessment as a screening test in 'low risk' pregnancies. One of the main aims of routine antenatal care is to identify the 'at risk' fetus in order to apply clinical interventions which could result in reduced perinatal morbidity and mortality. OBJECTIVES To assess the effects on obstetric practice and pregnancy outcome of routine Doppler ultrasound in unselected and low risk pregnancies. SEARCH STRATEGY The Cochrane Pregnancy and Childbirth Group Specialised Register of Controlled Trials and the Cochrane Controlled Trials Register were searched. Date of last search: September 1999 SELECTION CRITERIA Acceptably controlled trials of routine Doppler ultrasound (umbilical circulation and/or uterine circulation) in unselected or low risk pregnancies. DATA COLLECTION AND ANALYSIS Both reviewers assessed trial quality and extracted data. Authors of two trials were contacted for additional information. MAIN RESULTS Five trials were included which recruited 14,338 women. The methodological quality of the trials was generally good. Based on existing evidence, routine Doppler ultrasound examination in low risk or unselected populations did not result in increased antenatal, obstetric and neonatal interventions, and no overall differences were detected for substantive short term clinical outcomes such as perinatal mortality. There is no available evidence to assess the effect on substantive long term outcomes such as childhood neurodevelopment. There is no available evidence to assess maternal outcomes, particularly psychological effects. In two studies there were unexpected findings suggesting possible harmful effects, but the explanation for this is not clear, and further evaluation regarding the safety of Doppler ultrasound is required. REVIEWER'S CONCLUSIONS Based on existing evidence, routine Doppler ultrasound in low risk or unselected populations does not confer benefit on mother or baby. Future research should be powerful enough to address small changes in perinatal outcome, and should include evaluation of maternal psychological effects, long term outcomes such as neurodevelopment, and issues of safety.