Blood Group Analysis in Hemolytic Disease of the Newborn
The most likely set of blood groups in the mother and her newborn is E) O, Rh-negative mother and O, Rh-positive newborn. This combination represents the classic scenario for severe Rh incompatibility leading to hemolytic disease of the newborn (HDN).
Clinical Presentation Analysis
The case presents with several key findings indicating severe hemolytic disease:
- Newborn with bradycardia (pulse 60/min)
- Irregular and labored respirations
- Pallor with perioral cyanosis
- Anasarca (generalized edema)
- Hepatosplenomegaly
- Petechiae
- Severe anemia (hemoglobin 4 g/dL)
- Elevated reticulocyte count (18%)
- Positive direct antiglobulin (Coombs') test
These findings collectively point to severe hemolytic disease of the newborn, most commonly caused by Rh incompatibility.
Blood Group Analysis
Why O, Rh-negative mother and O, Rh-positive newborn?
Severity of the presentation: The severe anemia (Hgb 4 g/dL) with marked reticulocytosis (18%) indicates significant ongoing hemolysis. Rh incompatibility typically causes more severe HDN than ABO incompatibility 1.
Positive direct Coombs' test: This confirms antibodies are bound to the infant's red blood cells, consistent with maternal alloimmunization to fetal red cell antigens 1.
Clinical manifestations: The constellation of anasarca, hepatosplenomegaly, and severe anemia represents the classic presentation of hydrops fetalis, which is most commonly associated with Rh incompatibility 1.
Maternal-fetal blood group dynamics: When a mother is Rh-negative and the fetus is Rh-positive, maternal anti-D antibodies can cross the placenta and cause severe hemolysis of fetal red blood cells 1.
Why Not Other Blood Group Combinations?
Options A and B (A, Rh-positive mother): ABO incompatibility (mother type A with baby type O) typically causes milder disease than what is described in this case 2. While ABO-HDN can occur, it rarely presents with such severe anemia and hydrops.
Option C (A, Rh-negative mother and O, Rh-negative newborn): Without Rh incompatibility and with the baby being Rh-negative, there would be no anti-D mediated hemolysis. ABO incompatibility alone would be unlikely to cause this severe presentation.
Option D (O, Rh-positive mother and O, Rh-negative newborn): This combination would not cause HDN as the mother has Rh-positive blood and the baby has Rh-negative blood. There is no antigen in the baby that the mother lacks.
Pathophysiology of Rh Incompatibility
In Rh incompatibility:
- The RhD antigen is well developed by 6 weeks' gestation 1
- Maternal exposure to fetal RhD-positive blood cells (typically during delivery, but can occur earlier) leads to alloimmunization
- In subsequent pregnancies with an RhD-positive fetus, maternal anti-D IgG antibodies cross the placenta
- These antibodies bind to fetal RBCs, leading to hemolysis
- Severe anemia develops, potentially leading to hydrops fetalis
Clinical Implications
The severe presentation in this case indicates this is likely not the mother's first exposure to Rh-positive blood. The history of "gravida 2, para 1, aborta 1" suggests a prior pregnancy that could have sensitized the mother to the Rh antigen 1. The lack of prenatal care meant no prophylactic RhIg was administered, allowing unchecked antibody production.
The newborn requires immediate intervention, likely including:
- Phototherapy for hyperbilirubinemia
- Possible exchange transfusion to correct severe anemia and remove antibody-coated red cells
- Close monitoring for complications of severe HDN
Prevention Strategies
This case highlights the importance of:
- Prenatal blood typing for all pregnant women 1
- Administration of RhIg to Rh-negative mothers during pregnancy and after delivery of an Rh-positive infant
- Regular antibody screening during pregnancy for Rh-negative women
In conclusion, the clinical picture of severe hemolytic disease with hydrops fetalis, positive direct Coombs' test, and severe anemia is most consistent with Rh incompatibility from an O, Rh-negative mother and an O, Rh-positive newborn.