The antenatal assessment of utero-placental and feto-placental blood flow using Doppler ultrasound.

A brief discussion of the normal anatomy and physiology relevant to the understanding of blood flow is presented. After a review of previous attempts to measure blood flow in the utero-placental and feto-placental circulation, a description is given of the methods of obtaining Doppler signals from both maternal and fetal vessels. Some of the problems are presented. Flow velocity waveform (FVW) analysis is then presented in normal and in complicated pregnancies. FVW in pregnancies complicated by proteinuric hypertension have arcuate FVWs that demonstrate increased pulsatility and decreased velocities in diastole. These changes are also observed in most pregnancies complicated by intrauterine growth retardation and precede changes in the fetal circulation by several weeks. Impaired fetal circulation is demonstrated by low or decreased diastolic velocities in both the descending thoracic aorta and the umbilical artery. An attempt is made to give a pathophysiological understanding for these changes.