Maternal & Newborn · Topic 10 of 58
ABO Incompatibility in the Newborn
Start here
Tap any line to see why it matters
ABO Incompatibility in the Newborn
A type O mother's anti-A or anti-B IgG crosses the placenta and destroys the red cells of a type A or B baby. It can affect a first pregnancy, and jaundice in the first 24 hours is the warning.
Why it happens
Maternal anti-A or anti-B IgG destroys fetal red cells
A type O mother already has anti-A and anti-B antibodies. ABO disease is milder because fetal red cells carry less A and B antigen and early maternal IgM clears some fetal cells first. It is the most common immune hemolytic disease of the newborn, reported in about 2–5% of newborns.
What you'll see
Early jaundice, mild or no anemia
Labs & diagnostics
Cord blood type + direct Coombs (DAT) when the mother is type O
A bilirubin rise of 0.3 mg/dL per hour or more in the first 24 hours (0.2 mg/dL per hour after) suggests hemolysis and calls for a DAT. With a negative DAT but ongoing ABO hemolysis, the blood smear shows microspherocytes.
ABO or Rh disease?
ABO can hit a first pregnancy — and RhoGAM doesn't prevent it
| ABO | Rh | |
|---|---|---|
| Mother | Type O | Rh-negative |
| First pregnancy | Can be affected — antibodies already present | Needs prior sensitization |
| Severity | Usually milder | More severe |
| Direct Coombs (DAT) | Weakly positive or negative | Positive |
| RhoGAM | Doesn't prevent it | Prevents Rh(D) sensitization |
Red flags
Signs of acute bilirubin encephalopathy: report immediately
These are signs of acute bilirubin encephalopathy — report them immediately.
Treatment
Diaper only, eye shields on
Judge it by serum bilirubin, not skin colorTemperature about every 2 hours; feeds every 2–3 hours
Bilirubin still rising near the exchange level despite intensive phototherapy
Exchange transfusion for encephalopathy signs or bilirubin at the exchange threshold
More detail
Full phototherapy care is covered in Newborn Jaundice.
Nursing priorities
Teach the parents
Type O mother, type A or B baby — any pregnancy, even the first. Jaundice in the first 24 hours is pathologic: report it and expect a bilirubin level. RhoGAM doesn't prevent it.
Sources · Perinatal Anemia (MSD Manual Professional) · IgG Antibody Titer and Subtype in Hemolytic Disease of the Newborn (Transl Pediatr 2022) · Neonatal Hyperbilirubinemia (MSD Manual Professional) · Summary of the AAP 2022 Hyperbilirubinemia Guideline (Indian Pediatrics 2023) · Maternal-Newborn Nursing 24.2: Care of Common Problems in the Newborn (OpenStax) · RhoGAM Prescribing Information (DailyMed) · Newborn jaundice (MedlinePlus) · FAQs About the 2022 Hyperbilirubinemia Guideline (AAP) · Follow your facility's protocol for newborn bilirubin screening and phototherapy.
ABO Incompatibility in the Newborn
ABO incompatibility in the newborn is hemolysis that occurs most often when the mother is type O and the baby is type A or B, because the mother's anti-A or anti-B antibodies cross the placenta and destroy fetal red blood cells. A type O mother already carries these antibodies without any prior sensitization, so unlike Rh disease it can affect a first pregnancy, and RhoGAM does not prevent it. It is usually milder than Rh disease, with early jaundice and mild or no anemia. The hallmark is jaundice in the first 24 hours of life, which is pathologic and reported right away for a bilirubin level. When the mother is type O, the cord blood is tested for the baby's blood type and a direct Coombs test, which may be only weakly positive or even negative. Each bilirubin is plotted against the baby's age in hours. Phototherapy is the main treatment, IV immunoglobulin is added when bilirubin keeps rising toward the exchange level despite phototherapy, and lethargy, poor feeding or a high-pitched cry is reported immediately.
Loading questions…
Go further
- Commonly confusedPlacenta Previa vs Placental AbruptionPainless vs painful bleeding — the OB emergency discrimination.
- GuideATI Maternal Newborn Proctored Exam (CMS): What’s on It and How to StudyWhat the ATI Maternal Newborn proctored exam covers, from antepartum to the newborn, the level you need, and a ready-made study plan.
- GuideHow to Study for Med-Surg: Stop Memorizing, Start ConnectingMed-surg is the first course where memorizing stops working. Start every topic at the mechanism, climb from know-it to spot-it to act-on-it, and practice questions early at the right difficulty — with a real NGN bowtie to try in-page.
Ready to practice this topic?
Get a personalized study plan built around this topic — free to try, no card needed.