Model Answer
0 min readIntroduction
The ABO blood group system, discovered by Karl Landsteiner in 1901, is one of the most important blood type classifications used for transfusions. It’s based on the presence or absence of A and B antigens on the surface of red blood cells, and the corresponding antibodies in the plasma. Understanding this system is fundamental to safe blood transfusions and comprehending certain genetic incompatibilities, such as erythroblastosis foetalis, a potentially life-threatening condition arising from Rh incompatibility between mother and foetus. This condition, while less common now due to preventative measures, highlights the complexities of maternal-foetal immunology.
ABO Blood Group System
The ABO blood group system is determined by three alleles of a single gene: IA, IB, and i. IA and IB are codominant, while i is recessive. This leads to four main blood types:
- Type A: Genotypes IAIA or IAi – possesses A antigens on red blood cells and anti-B antibodies in plasma.
- Type B: Genotypes IBIB or IBi – possesses B antigens on red blood cells and anti-A antibodies in plasma.
- Type AB: Genotype IAIB – possesses both A and B antigens on red blood cells and neither anti-A nor anti-B antibodies in plasma.
- Type O: Genotype ii – possesses neither A nor B antigens on red blood cells and both anti-A and anti-B antibodies in plasma.
Blood transfusions must be compatible to avoid agglutination (clumping) of red blood cells, which can be fatal. For example, a person with Type A blood cannot receive Type B blood due to the presence of anti-B antibodies.
Erythroblastosis Foetalis (Hemolytic Disease of the Fetus and Newborn - HDFN)
Erythroblastosis foetalis, also known as Hemolytic Disease of the Fetus and Newborn (HDFN), is a condition caused by Rh incompatibility between a mother and her foetus. It primarily occurs when an Rh-negative mother carries an Rh-positive foetus.
Mechanism
The process unfolds as follows:
- Sensitization: During a previous pregnancy or through blood transfusion, an Rh-negative mother may be exposed to Rh-positive red blood cells. This exposure triggers an immune response, leading to the production of anti-Rh antibodies.
- Subsequent Pregnancy: In a subsequent pregnancy with an Rh-positive foetus, these anti-Rh antibodies cross the placenta and attack the foetus’s red blood cells.
- Hemolysis: This antibody-mediated destruction of foetal red blood cells (hemolysis) leads to anaemia, jaundice, and the release of bilirubin.
- Foetal Response: The foetus attempts to compensate for the anaemia by increasing erythropoiesis (red blood cell production), leading to the presence of erythroblasts (immature red blood cells) in the foetal circulation – hence the name "erythroblastosis".
Symptoms and Diagnosis
Symptoms in the foetus can range from mild anaemia to severe hydrops foetalis (generalized edema). Diagnosis involves:
- Maternal Blood Testing: Determining the mother’s Rh status and antibody levels (e.g., Coombs test).
- Foetal Blood Sampling: Assessing foetal anaemia and bilirubin levels.
- Ultrasound: Detecting signs of foetal anaemia and hydrops foetalis.
Treatment
Treatment options include:
- Intrauterine Transfusion: Transfusing Rh-negative red blood cells into the foetus to correct anaemia.
- Early Delivery: If the foetus is severely affected, early delivery may be necessary.
- Postnatal Exchange Transfusion: Replacing the infant’s blood with Rh-negative blood to remove antibodies and reduce bilirubin levels.
- Phototherapy: Used to reduce bilirubin levels in newborns.
Prophylaxis: The most effective prevention is the administration of Rh immunoglobulin (RhoGAM) to Rh-negative mothers at 28 weeks of gestation and within 72 hours of delivery if the baby is Rh-positive. This prevents sensitization by suppressing the mother’s immune response.
Conclusion
Both the ABO blood group system and erythroblastosis foetalis demonstrate the crucial role of genetics and immunology in human health. Understanding the principles governing blood types is essential for safe transfusions, while recognizing and managing Rh incompatibility is vital for preventing severe complications in foetuses and newborns. The widespread use of RhoGAM has dramatically reduced the incidence of HDFN, showcasing the power of preventative medicine in addressing genetic incompatibilities. Continued research into maternal-foetal immunology promises further advancements in protecting vulnerable populations.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.