Fetal hemoglobin has a higher affinity for oxygen than does maternal hemoglobin because it has a higher affinity for the allosteric regulator 2,3-bisphosphoglycerate.

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Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin due to structural differences in the globin protein subunits. Fetal hemoglobin has two gamma subunits, which bind oxygen more tightly than the beta subunits found in adult hemoglobin. The presence of 2,3-bisphosphoglycerate (2,3-BPG) actually decreases the affinity of hemoglobin for oxygen, rather than increasing it. This is because 2,3-BPG binds to a specific site on the beta subunits and stabilizes the T-state conformation, which has a lower affinity for oxygen. Fetal hemoglobin has lower levels of 2,3-BPG, which allows it to bind oxygen more tightly.

Fetal Hemoglobin Has a Higher Affinity for Oxygen Than Does