The Question is from neet-zoology body-fluids-and-circulation , and it was created by the author T SAILAJA

Question

A pregnant woman with blood group O negative and her fetus is Rh positive.  During her second pregnancy, which specific antibody crosses the placenta and causes erythroblastosis fetalis?

T SAILAJA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Rh incompatibility and erythroblastosis fetalis
 **Related Topics**: Blood group antigens, antibody types (IgG and IgM), placental transfer of antibodies, hemolytic disease of the newborn
 **Prerequisites**: Understanding of blood group systems (ABO and Rh), antibody structure and function, placental physiology
## SOLUTION PATHWAY
**Given Information**:
  * Mother's blood group: O negative (Rh-)
  * Fetus's blood group: Rh positive (Rh+)
  * Second pregnancy
  * Erythroblastosis fetalis is occurring
**Method & Steps**:
 1. Identify the antigen causing the problem.
  Reasoning: The mother is Rh-negative, meaning she lacks the Rh D antigen on her red blood cells.  The fetus is Rh positive, inheriting the Rh D antigen from the father. During the first pregnancy, some fetal Rh+ blood cells can enter the mother's circulation, leading to the production of anti-Rh D antibodies.
  Formula/Rule: None directly applicable, but understanding of immune response is crucial.
 2. Determine the type of antibody produced and its ability to cross the placenta.
  Working: The mother's immune system recognizes the Rh D antigen as foreign and produces antibodies against it.  IgG antibodies are the main type produced in this case, and importantly, IgG antibodies are small enough to cross the placenta.
  Key Point: IgM antibodies are larger and cannot cross the placenta effectively.
 3. Identify the antibody responsible for erythroblastosis fetalis in the second pregnancy.
  Result: In the second pregnancy, the maternal anti-D IgG antibodies cross the placenta and attack the fetal Rh+ red blood cells, causing hemolysis (destruction of red blood cells) and leading to erythroblastosis fetalis.
  Verification: The clinical presentation of erythroblastosis fetalis is consistent with the destruction of fetal red blood cells by maternal anti-D IgG antibodies.
 ## OPTION ANALYSIS
[A] :x: Anti-A IgM: This antibody is related to the ABO blood group system, not Rh incompatibility.
[B] :x: Anti-B IgG:  This antibody is also related to the ABO blood group system, not Rh incompatibility.
[C] ✓: Anti-D IgG: This is the correct antibody. It's specific to the Rh D antigen, is of the IgG type (which crosses the placenta), and causes the hemolytic disease.
[D] :x: Anti-O IgM: This is related to the ABO blood group system and IgM antibodies don't cross the placenta effectively.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing ABO and Rh incompatibility:  Understanding the distinct antigens and antibodies involved in each system is crucial.
  2.Assuming all antibodies cross the placenta: Only IgG antibodies can effectively cross the placental barrier.
 **Quick Tips**:
  1.Remember IgG crosses the placenta, IgM does not.
  2.Focus on the Rh D antigen as the key player in Rh incompatibility.

T SAILAJA · Answer

Anti-A IgM

T SAILAJA · Answer

Anti-B IgG

T SAILAJA · Answer

The correct Option is "Anti-D IgG"

T SAILAJA · Answer

Anti-O IgM

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