This study aims to measure the changes induced by packed red blood cell (PRBC) transfusion in the superior mesenteric artery (SMA) flow velocity and intestinal oxygenation indices in premature neonates. These changes will be measured in relation to feeding, before and after a blood transfusion. Overall reduction of intestinal perfusion is a risk factor for necrotizing enterocolitis (NEC) - a condition with significant mortality and long term morbidity. Identifying specific patterns of flow velocity and tissue oxygenation changes will allow for planning, studying and implementing risk avoidance and minimization strategies.