 Maternal blood contains adult hemoglobin composed of two alpha and two beta subunits (aka hemoglobin A or HbA; i.e., normal adult hemoglobin).Fetal blood contains fetal hemoglobin composed of two alpha and two gamma subunits (aka hemoglobin F or HbF; i.e., normal fetal hemoglobin).This difference in composition gives the different types of hemoglobin different chemical properties (in addition to the higher affinity HbF has for dissolved blood oxygen over HbA, allowing baby to extract oxygen from the mother's blood).