Nursing care
Rh vs ABO incompatibility: who is at risk, severity and Rho(D) immune globulin
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
Rh incompatibility affects an Rh-negative mother carrying an Rh-positive fetus; the first pregnancy is usually spared, but sensitisation can cause severe haemolysis in later pregnancies, and Rho(D) immune globulin prevents it. ABO incompatibility, classically a group O mother with a group A or B baby, is more common, can affect a first baby, is usually mild and has no preventive injection.
Lead with the first pregnancy question
The most differentiating point is whether a first baby can be affected. In Rh disease, the Rh-negative mother must first be exposed to Rh-positive fetal cells, usually at birth or after bleeding, miscarriage or procedures. MSD Manual notes the sensitising pregnancy itself usually has no complications; antibodies then threaten subsequent Rh-positive babies.
In ABO incompatibility, a group O mother typically already has anti-A and anti-B antibodies without any prior pregnancy. Some cross the placenta, so a first baby who is group A or B can develop haemolysis. If a stem describes a first baby with early jaundice and a group O mother, ABO is the better fit.
Prior sensitisation can change the Rh picture. An Rh-negative mother who had an earlier miscarriage, termination, ectopic pregnancy or unprotected birth may already carry anti-D antibodies, so even what looks like a first full pregnancy can be affected. The antibody screen at booking identifies this, which is why it is checked rather than assumed.
Severity: Rh can be severe, ABO is usually mild
Rh antibodies can cause profound fetal anaemia, heart failure and hydrops before birth, and rapid bilirubin rise afterward. MedlinePlus describes Rh incompatibility as able to cause very severe anaemia in the baby. Sensitised pregnancies are monitored closely by specialist teams for fetal anaemia, and some need intrauterine transfusion.
ABO incompatibility is the most common cause of mismatch but is usually not severe. It rarely causes significant disease before birth and typically shows as jaundice in the first day or two and mild anaemia. Phototherapy is often sufficient, though some infants need intravenous immunoglobulin or, rarely, exchange transfusion. Severity guides urgency, but both need bilirubin monitoring.
Where Rho(D) immune globulin fits
Rho(D) immune globulin prevents an unsensitised Rh-negative mother from forming her own anti-D antibodies. It is given routinely around 28 weeks, within 72 hours after birth of an Rh-positive baby, and after events that may mix blood, such as miscarriage, ectopic pregnancy, amniocentesis, abdominal trauma or bleeding. It does not treat an already sensitised mother.
No equivalent injection exists for ABO incompatibility, and Rho(D) immune globulin has no role in it. Nursing actions include confirming maternal blood group, Rh status and antibody screen, checking eligibility before administration and documenting the dose given. A mother who is Rh-positive does not receive it, even if her baby has jaundice.
Overlapping newborn findings and nursing care
Both conditions cause haemolysis, so both can produce jaundice within the first 24 hours, pallor, a positive direct antiglobulin test in many cases and a rising bilirubin. Jaundice alone cannot tell you which antibody is responsible; maternal and infant blood groups, antibody screening and the clinical course do that.
Nursing priorities overlap: early and repeated bilirubin checks as ordered, assessment for pallor, lethargy and poor feeding, effective feeding to support bilirubin excretion and phototherapy care. Report jaundice in the first day promptly. For Rh-sensitised infants, anticipate closer haematological follow-up because anaemia can develop or worsen in the weeks after birth.
Teach parents why repeated heel-prick bilirubin tests are needed, how phototherapy works and what to watch for at home, including increasing yellowness, sleepiness and poor feeding. Explain the result of any antibody testing in plain terms, and for Rh-negative mothers, reinforce the need for immune globulin in future pregnancies when indicated.
Work a hypothetical prenatal and newborn item
Take an original practice question: a first-time mother who is O positive gives birth to an A positive baby, who is jaundiced at 18 hours. A student asks whether the mother should have received Rho(D) immune globulin. The best response explains that the mother is Rh-positive, so the injection does not apply, and that ABO incompatibility can affect a first baby.
Contrast a mother who is A negative, antibody screen negative, after a first-trimester miscarriage. Here Rho(D) immune globulin is relevant because an unsensitised Rh-negative mother has had a potential exposure. Choosing the injection for the first mother or skipping it for the second are the tempting errors this comparison is designed to expose.
Sources and further reading
MSD Manual Professional: Erythroblastosis Fetalis. Rh sensitisation, unaffected sensitising pregnancy, fetal anaemia and hydrops, antibody screening and Rho(D) immune globulin timing.
MedlinePlus: Hemolytic disease of the newborn. ABO as the most common and usually milder mismatch, Rh causing severe anaemia, and phototherapy, IVIG and exchange transfusion.
MedlinePlus: Rh incompatibility. Who is at risk, first baby usually unaffected unless prior sensitisation, and immune globulin in pregnancy and after birth.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our maternity and newborn practice questions are the closest set to what this page covers.
Common questions
Can ABO incompatibility affect a first baby?
Yes. A group O mother usually already has anti-A and anti-B antibodies, so her first group A or B baby can develop haemolysis. It is usually mild.
Does Rho(D) immune globulin help a mother who is already sensitised?
No. It prevents antibody formation in an unsensitised Rh-negative mother. A sensitised pregnancy is managed with specialist fetal monitoring instead.
What is the timing of postpartum Rho(D) immune globulin?
It is given within 72 hours after birth when an unsensitised Rh-negative mother delivers an Rh-positive baby, following the prescriber's order and local protocol.