How long does ABO incompatibility last?
Last updated September 7, 2026.
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 do
- Watch the first days: Jaundice from ABO incompatibility often shows up within 24 hours of birth, so keep every early newborn checkup.
- Feed often: Frequent feeding helps clear bilirubin, so aim for 8 to 12 feeds a day and steady wet diapers.
- Keep the bilirubin recheck: Levels can keep rising after you go home, so go to the scheduled recheck even if your baby looks fine.
- Ask about anemia: Some babies need a blood count at 2 to 8 weeks because red cell breakdown can continue after the yellow color fades.
- Share your blood type: Tell your prenatal team your blood type and any history of newborn jaundice so cord blood testing can be arranged.
- Call the same day for red flags: Contact a clinician if your baby is hard to wake, feeds poorly, arches the back, or turns yellow on the belly or legs.
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