The prenatal recognition of the growth-retarded fetus is important because of the associated increased perinatal morbidity. Clinical methods of assessing fetal growth are disappointing and necessitate that a high-risk group be identified for more intensive surveillance. This review discusses the role of ultrasound biometry in establishing whether a fetus is small. Behavioral characteristics of the fetus may also be assessed using real-time ultrasound. The realization that not all small fetuses are a result of growth failure has led to the development of Doppler ultrasound to identify the fetus at risk. This paper focuses on the evidence supporting the selected use of Doppler ultrasound to investigate high-risk pregnancy.