Foetal Liver Embryogenesis and Foetal Functions

In foetal life, the liver takes up a very large portion of the abdominal cavity. In this stage, it does not perform the traditional digestive and filtration functions because nutrients are normally carried to the foetus from the mother via the placenta. Blood flow, rich in nutrients, arrives from the placenta to the foetus by the umbilical vein. It enters the abdomen at the umbilicus, passing upward along the free margin of the falciform ligament of the liver to its inferior surface. Blood flow in the umbilical vein has an oxygen saturation of approximately 80% compared with the 98% of the arterial adult circulation [2]. The ductus venosus, a little vein situated in the liver, carries some of this blood directly to the inferior vena cava, bypassing the liver circulation, where it joins blood from the lower trunk and extremities and from the liver. This flow arrives in the right atrium but is mostly diverted directly to the left atrium via a patent foramen oval in the atrial septum. From here, blood arrives to the left ventricle and ascending aorta to supply the coronary and cranial vascular beds [3,4]. Unlike in postnatal life, where the lungs receive the entire cardiac output, in foetal life, the collapsed lungs provide only 10% of the cardiac output [2]. In the presence of diminished nutrition or oxygenation, a greater volume of flow from the umbilical vein bypasses the liver and perfuses the head and neck of the foetus, privileging oxygen and nutrient delivery to the brain as part of the stated ‘brain-sparing’ effect [5,6]. In growth-restricted human foetuses, such brain-sparing responses are associated with cerebral vasodilation (measured using Doppler ultrasound as a low pulsatility index in the middle cerebral artery [3]) and with greater ductus venosus shunting [5,6]. Some of these adaptive changes seem to also occur in normally growing fetuses in late gestation; a large variation in the proportion of placental blood perfusing or bypassing the liver have been described in in such foetuses [7].