Hemoglobin is the oxygen-carrying substance in red blood cells. Fetal hemoglobin (HbF) is the type of hemoglobin produced by a fetus's body.
At birth, babies typically have half fetal hemoglobin and half adult hemoglobin (HbA). After birth, HbF is gradually replaced by HbA.
Some people with sickle cell disease continue to produce some HbF, which helps protect them from more severe complications of the disease.
WebMD Medical Reference from Healthwise