[Fetal circulation--from passive knowledge to current hemodynamics].

BACKGROUND

Modern technology, especially ultrasound, has made foetal medicine a rapidly expanding field. The aim of the present review is to focus at the traditional knowledge of foetal circulation, which has recently been reassessed and expanded to serve our new patient, the human foetus.

MATERIAL AND METHODS

Based on literature published mainly over the last 10 years, specific mechanisms of the foetal circulation are discussed, particularly the three foetal shunts and the placental circuit.

RESULTS

The foetal circulation has capacity to compensate for considerable cardiovascular abnormalities and to redistribute circulation to meet shortage in resources. The circulatory mechanisms described in animal foetuses also operate in the human foetus, but with notable differences. The ductus venosus shunts 20-30% of the umbilical blood in the human foetus compared to 50% in the foetal lamb. The foramen ovale receives less (18-34% of the combined cardiac output) and the lungs more blood (13-25%) in the human foetus than in the foetal lamb. The isthmus aortae represents a watershed area reflecting the redistribution of blood during increased peripheral impedance and hypoxemia.

INTERPRETATION

The expanded knowledge in human foetal circulation promises a more differentiated evaluation than the Doppler examination of the umbilical and middle cerebral artery offers at the moment.