fetal hemoglobin (HgbF), the predominate hemoglobin found in later pregnancy, composed of two alpha chains and two beta chains physiologically different from adult hemoglobin A (HgbA) in that, at any given oxygen tension, HgbF has a higher oxygen affinity and oxygen saturation than HgbA. Thus, although the partial pressure of oxygen in the fetal arterial blood supply is only 20 to 25 mm Hg, the fetus remains adequately oxygenated in utero and the early neonatal period.
