Management of Rh Negative Baby Born to Rh Negative Mother
An Rh negative baby born to an Rh negative mother faces essentially no risk of hemolytic disease, regardless of the father's Rh status, because the baby inherited Rh negative status from both parents and maternal antibodies cannot form against antigens the baby does not possess.
Understanding the Fundamental Immunology
The critical point is that hemolytic disease requires maternal antibodies directed against fetal red blood cell antigens. When both mother and baby are Rh negative:
- The baby's red blood cells lack the RhD antigen entirely 1
- Even if the mother were previously sensitized (which is unlikely given her Rh negative status), her anti-D antibodies would have no target on the baby's RhD-negative red cells 2
- Maternal alloimmunization only occurs when an Rh negative mother is exposed to Rh positive fetal cells, triggering antibody production against the foreign D antigen 3, 4
Why This Baby Is Not At Risk
The baby cannot have hemolytic disease because there is no antigen-antibody mismatch. Here's the genetic reality:
- An Rh negative mother (dd genotype) can only pass a "d" allele to her offspring 5
- If the baby is Rh negative, the baby received "d" from both parents (dd genotype) 4
- The father's Rh positive status is irrelevant in this scenario because the baby did not inherit his D antigen 1
Approximately 90% of fetomaternal hemorrhage occurs during delivery, meaning the first baby is typically born before significant maternal antibody production occurs 1. However, this protection mechanism is unnecessary here since no incompatibility exists.
Clinical Management at Delivery
Despite the absence of risk, standard newborn assessment should still occur:
- Do NOT perform a direct antiglobulin test (Coombs' test) on cord blood if the baby's blood type is confirmed Rh negative, as there is no indication for this test when both mother and baby are Rh negative 1
- Monitor for jaundice using standard newborn protocols (assessment every 8-12 hours), though hemolytic disease is not a concern 1
- If jaundice develops, it would be due to physiologic causes or other etiologies (ABO incompatibility, G6PD deficiency, etc.), not RhD incompatibility 6
Maternal RhIg Prophylaxis Considerations
The mother does NOT require postpartum RhIg administration because:
- RhIg is only indicated when an Rh negative mother delivers an Rh positive infant 3, 2
- The purpose of RhIg is to prevent sensitization to Rh positive fetal cells 2
- When the baby is Rh negative, there are no Rh positive cells to cause sensitization 3
The standard protocol of administering RhIg within 72 hours of delivery of an Rh positive infant does not apply here 3, 2.
Common Pitfall to Avoid
Do not reflexively administer RhIg simply because the mother is Rh negative. The critical determining factor is the baby's blood type, not just the mother's Rh status or the father's potential contribution 3. RhIg administration carries low risk, but unnecessary medication administration should be avoided when there is no clinical indication 3.
Future Pregnancy Implications
This mother remains at standard risk for future pregnancies:
- If she conceives another Rh negative baby, the same low-risk scenario applies 4
- If she conceives an Rh positive baby in the future, standard RhIg prophylaxis protocols would apply (28 weeks gestation and postpartum) 3
- She has no history of sensitization from this pregnancy since no incompatibility occurred 1