Fetal hemoglobin, or foetal haemoglobin, (also hemoglobin F or HbF) is the main oxygen transport protein in the fetus during the last seven months of development in the uterus and in the newborn until roughly 6 months old. 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.
In newborns, fetal hemoglobin is nearly completely replaced by adult hemoglobin by approximately 6 months postnatally. In adults, fetal hemoglobin production can be reactivated pharmacologically, which is useful in the treatment of diseases such as sickle-cell disease.
Read more about Fetal Hemoglobin: Overview, Distribution, Structure and Genetics