Question:medium
In which one of the following combinations, ABO incompatibility is most common?
In which one of the following combinations, ABO incompatibility is most common?
Show Hint
ABO hemolytic disease of the newborn needs a mother who is blood group O, since only her anti-A and anti-B antibodies are mostly IgG.
Updated On: Jul 7, 2026
- Mother's group 'A' and father's group 'O'
- Mother's group 'A' and father's group 'B'
- Mother's group 'O' and father's group 'A'
- Mother's group 'B' and father's group 'AB'
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
This question is really testing whether we know which parent's blood group matters most in ABO incompatibility, and why.
Step 2: Key Approach:
Remember that only IgG antibodies pass through the placenta from mother to baby. So we should look first at which blood group makes IgG antibodies against A and B antigens, then match that to the given combinations.
Step 3: Detailed Explanation:
Group O people are unusual in that their natural anti-A and anti-B antibodies are largely the IgG kind, built to cross into the fetal blood stream. Group A people make anti-B, and group B people make anti-A, but these are mostly the larger IgM kind that stays in the mother's own blood.
So the danger combination needs an O group mother carrying a fetus who has inherited an A or B antigen from the father. Checking the four combinations, only mother O with father A puts the mother in this at risk group. The other three combinations all keep the mother as group A or B, where her antibody is the placenta-blocked IgM type.
The printed key for this question names mother A, father B as the answer, but that combination cannot produce a placenta crossing IgG attack, since a group A mother's anti-B stays IgM. We flag this and go with the combination supported by the underlying immunology instead.
Step 4: Final Answer:
Mother group O with father group A is the combination where ABO incompatibility is most common.
This question is really testing whether we know which parent's blood group matters most in ABO incompatibility, and why.
Step 2: Key Approach:
Remember that only IgG antibodies pass through the placenta from mother to baby. So we should look first at which blood group makes IgG antibodies against A and B antigens, then match that to the given combinations.
Step 3: Detailed Explanation:
Group O people are unusual in that their natural anti-A and anti-B antibodies are largely the IgG kind, built to cross into the fetal blood stream. Group A people make anti-B, and group B people make anti-A, but these are mostly the larger IgM kind that stays in the mother's own blood.
So the danger combination needs an O group mother carrying a fetus who has inherited an A or B antigen from the father. Checking the four combinations, only mother O with father A puts the mother in this at risk group. The other three combinations all keep the mother as group A or B, where her antibody is the placenta-blocked IgM type.
The printed key for this question names mother A, father B as the answer, but that combination cannot produce a placenta crossing IgG attack, since a group A mother's anti-B stays IgM. We flag this and go with the combination supported by the underlying immunology instead.
Step 4: Final Answer:
Mother group O with father group A is the combination where ABO incompatibility is most common.
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