When a Baby's Blood Type Doesn't Match His Mom's

ABO incompatibility is rarely serious but can cause jaundice or anemia

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After waiting nine long months to meet their baby, little could be more delightful for proud new parents than taking stock of whose ears he got, whose dimpled chin, whose extraordinarily long and slender toes. But what about his blood type? While it may be just fine that an infant's hair color, say, is different than his mom's (even if she was secretly hoping he'd inherit her strawberry blond curls), it sometimes is a different story if an infant's blood type isn't the same as his mother's. In that case, he could be at risk for a condition known as ABO blood type incompatibility, a type of illness known as a hemolytic disease of the newborn (HDN). (Another example of an HDN occurs when a mother's blood is Rh-negative and her baby is Rh-positive. Rh factor incompatibility is screened for during pregnancy; an expectant mom can be given a shot to deflect problems.)

In the past, an HDN (clinically known as erythroblastosis fetalis) could put a baby's health at serious risk. In fact, at one time HDNs were a major cause of death for new babies. Now that medical researchers better understand the mechanisms that cause HDNs, they aren't nearly as threatening. If you're a new mom whose baby's blood type is different from yours, here's what you need to know about ABO incompatibility.

The ABCs of ABO Incompatibility

The letters A, B, and O refer to the four blood types—A, B, AB, and O. Blood type is determined based on proteins on the surface of red blood cells. These proteins are potential antigens—substances the immune system doesn't recognize. For protection, the immune system will create antibodies to fight off the unfamiliar protein. These antibodies can cross the placenta, where they will break down the baby's red blood cells after she's born.

The reason a baby's blood type isn't always the same as his mother is that blood type is based on genes from each parent. So, for example, a mother who is type O and a father who is type A could have a child who is type A. The reason the baby wouldn't have type O blood, like his mom, is because the gene for O is recessive.

Not all non-matching combinations of blood types are problematic. ABO incompatibility can occur only if a woman with type O blood has a baby whose blood is type A, type B, or type AB. If a baby is type O there won't be a problem with a negative immune response because type O blood cells don't have immune-response triggering antigens.

How ABO Incompatibility Is Treated

The most common problem caused by ABO incompatibility is jaundice. Jaundice occurs when there's a buildup of an orangish-red substance in the blood called bilirubin that's produced when red blood cells break down naturally. If more red blood cells are broken down at once than is normal, the bilirubin that results will deposit fatty tissue under the skin, causing the yellowish hue of the skin and whites of the eyes that are the tell-tale symptom of jaundice.

Not every baby with ABO incompatibility will develop jaundice, and not every baby with jaundice will require extensive treatment. It will depend on how much bilirubin collects in the baby's blood. Some infants with mild jaundice will get better on their own simply by being fed more often. A temporary increase in feedings will lead to an increase in bowel movements, which is how excess bilirubin exits the body. Moms who breastfeed may need to supplement their baby's diet with a formula for a few days if nursing alone doesn't do the trick.

For infants whose jaundice is more severe, phototherapy, or light therapy, is effective. The baby's skin is exposed to light waves that transform the bilirubin into a substance that can pass through the baby's system. The baby will literally be placed under the light wearing just a diaper and soft eye patches. Instead of, or in addition to, phototherapy a baby with jaundice may be treated with biliblanket which uses fiber optics to break down bilirubin.

In rare cases, a baby with an HDN will need to be treated with a type of blood transfusion called an exchange transfusion. This is when a portion of a baby's blood is replaced with type O blood. And a child who becomes severely anemic as a result of an HDN may need a more traditional transfusion in which he's given extra blood to replace blood that's lost.

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9 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hemolytic Disease of the Newborn. U.S. National Library of Medicine. U.S. Department of Health and Human Services.

  2. RH Disease. Stanford Children’s Hospital.

  3. Hemolytic Disease of the Newborn. U.S. National Library of Medicine. U.S. Department of Health and Human Services.

  4. Kanchan T, Krishan K. Blood Grouping in Payne-James J, Byard RW (Editors).

    Encyclopedia of Forensic and Legal Medicine (Second Edition). 2016;425-432.


  5. Newborn jaundice. U.S. National Library of Medicine. U.S. Department of Health and Human Services.

  6. Jaundice in healthy newborns. Rady Children’s Hospital San Diego. 2015.

  7. Jaundice. Centers for Disease and Control Prevention. 2018.

  8. Yurdadok M. Phototherapy in the newborn: what’s new? Journal of Pediatric and Neonatal Individualized Medicine 2015;4(2):e040255. doi:10.7363/040255

  9. Hemolytic Disease of the newborn. University of Rochester Medical Center.

Additional Reading
  • Avery's Diseases of the Newborn. 9th ed. Philadelphia, PA: Elsevier Saunders, 2012.

  • Dean L. Blood Groups and Red Blood Cell Antigens, "Hemolytic Disease of the Newborn," National Center for Biotechnology Information, 2005.