Fetal hemoglobin, or Foetal haemoglobin in British English, (also hemoglobin F or HbF) is the main oxygen transport protein in the fetus uring the last seven months of development in the uterus. Functionally, fetal hemoglobin differs most from adult hemoglobin in that it is able to bind oxygen with greater affinity than the adult form, giving the developing fetus better access to oxygen from the mother's bloodstream.