At 30 weeks' gestation, half of the approximately 110 ml/kg total blood volume (BV) of the feto-placental circulation is in the fetus, rising, by term, to about 90 ml/kg. In preterm infants at birth, subnormal blood volume is the rule, because of immediate cord clamping. Blood volume, typically 50-60 ml/kg during critical care, limits systemic oxygen (O2) transport and, because of shunting, causes hepato-splanchnic ischaemia and impaired lung function. Haemoconcentration results from plasma extravasation because of vascular endothelial damage. This elevates the haematocrit, masking the red cell lack. By allowing placental transfusion at birth, delaying cord clamping by 30-60 seconds, initial oligovolaemia is obviated, and post-natal lung adaptation greatly facilitated. The complications and costs of care can thereby be much reduced. Losses of haemopoietic stem cells are reduced, vital for haematologic and immunologic constitution and for response to haemopoietic growth factors. Further work is urgently needed to determine how to optimize this vital opportunity in preventive medicine in perinatology, with the objective of preventing complications, and reducing costs of all kinds, in management of the infant born preterm.