Behavioural states and cardiovascular dynamics in the human fetus; an overview

Behavioural state dependent changes occur in the circulation of the normally developing human fetus at term. During fetal behavioural state 2F (active sleep), there seems to be preferential blood flow through the ductus venosus and foramen ovale into the left heart. Increased left ventricular output of well-oxygenated blood during fetal behavioural state 2F will be necessary to meet the raised energy demands both at cerebral and trunk level as demonstrated by reduced pulsatility index values in the descending aorta, renal artery and intracranial arteries during this behavioural state. The limited studies in IUGR suggest behavioural state independency in the descending aorta and internal carotid artery which may be attributed to the fetus being incapable of adjusting its circulation to the existing behavioural state in the presence of circulatory centralization.