The blood type mismatch itself lasts for life, but the illness it causes is short, and newborn jaundice from ABO incompatibility usually clears within one to two weeks.
Blood type is genetic, so an ABO mismatch between a parent and baby, or between a donor and a recipient, does not go away. What is temporary is the antibody reaction against red blood cells. In a newborn, jaundice from ABO incompatibility typically starts in the first day of life, peaks around days 3 to 5, and fades within one to two weeks, and phototherapy shortens that further. Mild anemia can last several more weeks while the maternal antibodies clear from the baby's blood, which is why some babies get a blood count at a follow-up visit. A newborn who is very sleepy, feeding poorly, or yellow down to the belly or legs should be seen by a clinician the same day.
What to expect
Common questions
How long does ABO incompatibility last?
ABO incompatibility itself is permanent, because blood type is set by your genes and never changes. What is temporary is the reaction it can cause. In a newborn, antibodies from the birthing parent break down some of the baby's red blood cells, so jaundice usually appears in the first 24 to 36 hours, peaks around days 3 to 5, and settles within one to two weeks. Phototherapy speeds that up, and severe cases are rare. Mild anemia can linger for several weeks until the borrowed antibodies clear, so a repeat blood count is sometimes needed. In a transfusion, an ABO mismatch triggers a reaction within minutes, the transfusion is stopped immediately, and the acute illness is treated over hours to days.