Erythrocyte 2,3-diphosphoglycerate and associated haematological parameters during the menstrual cycle and pregnancy.

Erythrocyte 2,3-diphosphoglycerate (2,3-DPG) and associated haematological parameters were measured throughout the normal menstrual cycle, in each trimester of pregnancy and on the third day post partum. There was no significant change during the menstrual cycle but the 2,3-DPG concentration was increased early in pregnancy, and thereafter gradually decreased. Although other metabolic changes are likely to contribute to the increase in 2,3-DPG concentration, it is concluded that 'functional anaemia', secondary to increased oxygen demand, is a more important stimulus than the decrease in haemoglobin concentration. The implications of a decreased oxygen affinity of haemoglobin, secondary to the rise in 2,3-DPG concentration, are discussed in relation to anaemia and blood transfusion in pregnancy.