Doppler ultrasound in the fetus: a review of current applications.

With the recent introduction of Doppler pulsed and continuous wave as well as color-flow mapping, assessment of blood velocity in the human fetus has added a new dimension to fetal assessment. Although investigators initially examined blood flow in the descending aorta and umbilical vein, there was a wide variation in normal values because of the difficulty of accurately measuring the area of the vessels, a requirement for computation of blood volume. Using duplex sector scanners, velocity and blood flow have been obtained from the right and left ventricular chambers and aortic and pulmonic outflow tracts. At the present time the clinical application of the latter measurements is still under investigation. Doppler color-flow mapping appears to be promising for elucidation of abnormal flow in fetuses suspected of having structural and/or functional cardiovascular disease. Because of the difficulty in computing volume flow due to the above mentioned factors, more recently investigators have examined angle independent parameters of blood velocity from the aorta, carotid and umbilical arteries in an attempt to quantify peripheral resistance. This latter technique appears to be promising for elucidation of placental pathology as is found in a number of fetal and placental diseases.