Neonatology: twin-twin transfusion syndrome: practice question

A Pediatrics 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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Pediatrics · Neonatology: twin-twin transfusion syndrome

Sample item

Monochorionic twins are born. Twin A is small, pale with haemoglobin 11 g/dL and was in an oligohydramnios sac. Twin B is large and plethoric with haemoglobin 23 g/dL and was in a polyhydramnios sac. What explains this?

AUnbalanced blood flow through anastomoses in a shared placentaBFetomaternal haemorrhage in Twin A onlyCPlacental insufficiency affecting two separate placentasDRh alloimmunisation of Twin A

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

The answer and the reasoning

A. Unbalanced blood flow through anastomoses in a shared placenta

In twin-twin transfusion syndrome, arteriovenous anastomoses in a shared monochorionic placenta transfer blood from the donor to the recipient. The donor becomes anaemic, growth-restricted and oligohydramnic, while the recipient becomes polycythaemic, hypervolaemic and polyhydramnic. The recipient may need a partial exchange transfusion.

Option by option

A. Unbalanced blood flow through anastomoses in a shared placenta (correct)
Correct. A net flow of blood from donor to recipient through shared placental vessels explains both twins.
B. Fetomaternal haemorrhage in Twin A only
Fetomaternal haemorrhage would not make the other twin polycythaemic.
C. Placental insufficiency affecting two separate placentas
A dichorionic pair has two placentas and no communicating vessels for transfusion.
D. Rh alloimmunisation of Twin A
Rh alloimmunisation would cause haemolysis in both fetuses, not polycythaemia in one.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is A, Unbalanced blood flow through anastomoses in a shared placenta. In twin-twin transfusion syndrome, arteriovenous anastomoses in a shared monochorionic placenta transfer blood from the donor to the recipient.

Why is "Fetomaternal haemorrhage in Twin A only" not the answer?

Fetomaternal haemorrhage would not make the other twin polycythaemic.

Why is "Placental insufficiency affecting two separate placentas" not the answer?

A dichorionic pair has two placentas and no communicating vessels for transfusion.

Why is "Rh alloimmunisation of Twin A" not the answer?

Rh alloimmunisation would cause haemolysis in both fetuses, not polycythaemia in one.

What concept does this question test?

It tests Neonatology: twin-twin transfusion syndrome in Pediatrics. The donor becomes anaemic, growth-restricted and oligohydramnic, while the recipient becomes polycythaemic, hypervolaemic and polyhydramnic. The recipient may need a partial exchange transfusion.

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 Neonatology: twin-twin transfusion syndrome?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.