The oxygen consumption of the placenta and foetal membranes in the sheep

Abstract

1. In anaesthetized sheep near term the O₂ uptake of the foetus from the placenta was reduced to zero either by replacing the foetus with a mechanical pump, or by ventilation of the foetus after delivery or in utero. When umbilical arterial and venous PO₂ were made equal, they were much less than maternal arterial PO₂.2. This difference in PO₂ was attributed to O₂ consumption both within the placental cotyledons and the extra‐cotyledonary foetal membranes.3. The foetal membranes and cord in the sheep are supplied by branches of umbilical blood vessels and constitute an oxygen‐consuming by‐pass on the foetal side of the placenta.4. The O₂ consumption of individual placental cotyledons was measured in vivo.5. The combined O₂ consumption of the whole placenta and foetal membranes in vivo was a considerable fraction of foetal O₂ consumption.6. The consequences of these observations are discussed in relation to O₂ transfer across the placenta.