Hemoglobin F (HbF) contains two globin alpha chains and two globin gamma chains. It is the main form of hemoglobin in the fetus during the last seven months of intrauterine development and in the half year of postnatal life. In adults it normally makes up less than one percent of all hemoglobin. This term refers to an increase in HbF above this limit. In beta thalassemia major, it may represent over 90 percent of all hemoglobin, and in beta thalassemia minor it may make up between 0.5 to 4 percent. The phenotype is HP_0011904 (Persistence of hemoglobin F). Also known as: Increased haemoglobin F, Increased hemoglobin F, Persistence of HbF, Persistence of haemoglobin F.