Complications of pregnancy: Kell alloimmunisation: practice question

A OBG question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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OBG · Complications of pregnancy: Kell alloimmunisation

Sample item

A woman with anti-Kell antibodies has a fetus with severe anaemia and hydrops, although her antibody titre is only modest and the amniotic fluid bilirubin level is low. Which mechanism best explains these findings?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Antibody suppression of fetal erythroid progenitor cells

Kell antigens are expressed on early erythroid progenitor cells, so anti-Kell antibody suppresses erythropoiesis in addition to causing haemolysis. Anaemia can be severe despite low titres and low bilirubin, so amniotic fluid spectrophotometry and titres are unreliable. Middle cerebral artery Doppler is used to monitor these fetuses.

Option by option

  • A. Placental transfer of maternal IgM antibodies to the fetus

    IgM does not cross the placenta; IgG antibodies cause the disease.

  • B. Aplastic crisis from a coexisting parvovirus infection

    Parvovirus is a separate infective cause and is unrelated to Kell antibodies.

  • C. Antibody suppression of fetal erythroid progenitor cells (correct)

    Correct. Anti-Kell destroys erythroid precursors, causing anaemia out of proportion to haemolysis markers.

  • D. Massive intravascular haemolysis overwhelming the fetal liver

    Haemolysis would raise amniotic bilirubin, which is low here.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this OBG question

What is the answer to this OBG question?

The best answer is C, Antibody suppression of fetal erythroid progenitor cells. Kell antigens are expressed on early erythroid progenitor cells, so anti-Kell antibody suppresses erythropoiesis in addition to causing haemolysis.

Why is "Placental transfer of maternal IgM antibodies to the fetus" not the answer?

IgM does not cross the placenta; IgG antibodies cause the disease.

Why is "Aplastic crisis from a coexisting parvovirus infection" not the answer?

Parvovirus is a separate infective cause and is unrelated to Kell antibodies.

Why is "Massive intravascular haemolysis overwhelming the fetal liver" not the answer?

Haemolysis would raise amniotic bilirubin, which is low here.

What concept does this question test?

It tests Complications of pregnancy: Kell alloimmunisation in OBG. Anaemia can be severe despite low titres and low bilirubin, so amniotic fluid spectrophotometry and titres are unreliable. Middle cerebral artery Doppler is used to monitor these fetuses.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Complications of pregnancy: Kell alloimmunisation?

Learn management algorithms as steps: PPH, eclampsia, ectopic pregnancy. Then use the flashcards and the other OBG questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.