Haemodynamic evaluation of the first trimester fetus with special emphasis on venous return.

Knowledge of the fetal circulation is a prerequisite for understanding the physiological behaviour of the developing fetus. In this overview dealing with Colour and Power Doppler ultrasound findings in the first trimester of pregnancy and its pathophysiological background, we aim to report on the methodological aspects, normal blood flow waveform patterns, normal reference values for haemodynamic parameters and potential clinical applications for both arterial and venous flow information (umbilical artery, descending aorta, middle cerebral artery, umbilical vein, inferior vena cava, ductus venosus) and atrioventricular valves. Particular emphasis is devoted to the venous return to the heart. Alterations in venous waveforms, particularly in the ductus venosus, are correlated with the pathophysiology of some fetal diseases and are suggested as a promising tool for the screening of cardiac impairment and as an alternative method for fetal biophysical surveillance.