Status of the oxygen transport system of hemoglobin in physiological pregnancy and pregnancy complicated by iron deficiency anemia

The oxygen-binding properties of Hb molecule are unchanged in the third trimester of normal pregnancy and in pregnancy complicated by slight iron-deficiency anemia. Hb affinity to oxygen in whole blood is formed under the effect of the three main ligands H+, CO2, and 2,3-DPH. The development of hypocapnia in pregnant women results in elevation of pH values, reduction of pCO2, increase of intraerythrocytic 2,3-DPH concentration by 15-18%. Variously directed effects of H+, CO2, and 2,3-DPH on Hb affinity to O2 result in normal P50 values and therefore the Hb-O2 dissociation curve is not shifted to the right. Thus, in pregnant women with alkalosis 2,3-DPH effect on Hb affinity to oxygen completely eliminates H+ and CO2 effects but not compensates for Hb deficiency in the blood.