Red Cell 2,3-Diphosphoglycerate and Hemoglobin-Oxygen Affinity During Diabetic Pregnancy

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Abstract
Factors involved in blood oxygen transport were measured serially in the first, second and third trimester of pregnancy in 23 insulin-dependent diabetic women. Twenty-six non-pregnant diabetic patients served as a reference group. Diabetic pregnancy was associated with relative anemia, a significant increase in arterial pH, and hypocap-nia. The concentration of red cell 2,3-diphosphoglycerate was significantly higher in the first trimester of diabetic pregnancy compared with non-pregnant diabetics (median value 16.4 vs. 15.0 μmol/g hemoglobin, p>0.02) and increased gradually from the first to the third trimester (16.4 to 17.2 μmol/g hemoglobin, p1c concentration decreased simultaneously from 8.1% to 7.3% (p 0.01). In spite of the increase in red cell 2,3-diphosphoglycerate content and the decrease in hemoglobin A1c, factors known to reduce hemoglobin oxygen affinity, the position of the oxyhemoglobin dissociation curve remained unchanged during diabetic pregnancy: P50 at actual pH in the first trimester, was 26.0 mmHg; in the second trimester, 26.9 mmHg, and in the third trimester, 26.8 mmHg (NS). These values of P50 at actual pH were identical with the value in the non-pregnant group (26.6 mmHg). Other factors influencing hemoglobin oxygen affinity, such as hemoglobin concentration, hydrogen ion concentration and arterial oxygen saturation remained unchanged during diabetic pregnancy. The observations suggest that an unknown factor which increases hemoglobin oxygen affinity and to which the increased level of red cell 2,3-diphosphoglycerate may be compensatory, is operating in diabetic pregnancy.