Final answer:
Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin because of structural differences in its subunits, allowing efficient oxygen transfer from maternal blood with lower O2 pressure in the placenta.
Step-by-step explanation:
Fetal hemoglobin has a higher affinity for O2 than adult hemoglobin due to a structural difference in its subunits. Fetal hemoglobin's oxygen-binding curve exhibits an increased affinity for O2 at lower partial pressures, which is critical for effectively transferring oxygen from maternal blood with relatively low O2 pressure in the placenta. The presence of 2,3-bisphosphoglycerate (2,3-BPG) influences the affinity of hemoglobin for oxygen, but fetal hemoglobin's reduced affinity for 2,3-BPG compared to adult hemoglobin contributes to its higher oxygen affinity, helping the fetus to efficiently pick up oxygen carried in maternal blood.