Complications of pregnancy: twin anaemia-polycythaemia sequence: 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: twin anaemia-polycythaemia sequence

Sample item

In monochorionic twins at 28 weeks, amniotic fluid volumes are similar, but the middle cerebral artery peak velocity is raised in one twin and low in the other. At birth one twin is pale (haemoglobin 8 g/dL) and the other plethoric (haemoglobin 24 g/dL). Which diagnosis fits?

ASelective fetal growth restrictionBTwin reversed arterial perfusion sequenceCTwin-twin transfusion syndromeDTwin anaemia-polycythaemia sequence

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

The answer and the reasoning

D. Twin anaemia-polycythaemia sequence

TAPS results from tiny unidirectional anastomoses that slowly shift blood from donor to recipient, without the oligohydramnios-polyhydramnios sequence of TTTS. The haemoglobin difference and discordant middle cerebral artery velocities are the diagnostic clues.

Option by option

A. Selective fetal growth restriction
Selective growth restriction shows a weight discordance, not haemoglobin discordance of this type.
B. Twin reversed arterial perfusion sequence
TRAP involves an acardiac twin perfused by a pump twin.
C. Twin-twin transfusion syndrome
TTTS requires oligohydramnios in the donor and polyhydramnios in the recipient.
D. Twin anaemia-polycythaemia sequence (correct)
Correct. Large haemoglobin discordance without liquor discordance defines TAPS.

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.

Questions about this OBG question

What is the answer to this OBG question?

The best answer is D, Twin anaemia-polycythaemia sequence. TAPS results from tiny unidirectional anastomoses that slowly shift blood from donor to recipient, without the oligohydramnios-polyhydramnios sequence of TTTS.

Why is "Selective fetal growth restriction" not the answer?

Selective growth restriction shows a weight discordance, not haemoglobin discordance of this type.

Why is "Twin reversed arterial perfusion sequence" not the answer?

TRAP involves an acardiac twin perfused by a pump twin.

Why is "Twin-twin transfusion syndrome" not the answer?

TTTS requires oligohydramnios in the donor and polyhydramnios in the recipient.

What concept does this question test?

It tests Complications of pregnancy: twin anaemia-polycythaemia sequence in OBG. The haemoglobin difference and discordant middle cerebral artery velocities are the diagnostic clues.

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: twin anaemia-polycythaemia sequence?

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.