Red Cell 2,3‐Diphosphoglycerate and Hemoglobin‐Oxygen Affinity During Normal Pregnancy

. The concentration of red cell 2,3‐diphosphoglyce‐rate (2,3‐DPG), hemoglobin‐oxygen affinity and other oxygen transport variables were determined during first, second and third trimester of normal pregnancy as well as 3 months post partum in 18 healthy women. The median concentration of red cell 2,3‐DPG increased significantly from the first to the third trimester (16.1 to 17.0 μmol/gHb, p>0.01), whereas 2,3‐DPG decreased significantly post partum (p>0.01). Normal pregnancy was also associated with relative anemia, a significant increase in arterial pH, hypocapnia and hypophosphatemia. The difference in hemoglobin concentration from the first trimester to 3 months post partum was correlated inversely with the difference in red cell 2,3‐DPG content (r= 0.52, p>0.05). In spite of the variations in red cell 2,3‐DPG, hemoglobin‐oxygen affinity expressed as p 50 at actual pH remained unchanged during pregnancy and post partum. The study suggests that the increased level of 2,3‐DPG during pregnancy may in part represent compensation for physiologic anemia and also compensate for a factor leading to increased hemoglobin‐oxygen affinity during pregnancy.