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Difficulty: HardObstetric Complications

Match each ultrasound or clinical finding in a multifetal gestation to the most likely associated monochorionic twin complication.

  • Monochorionic diamniotic gestation with maximum vertical pockets of 9 cm in one sac and 1.5 cm in the otherTwin-twin transfusion syndrome (TTTS)
  • Monochorionic diamniotic gestation with normal amniotic fluid volumes but discordant middle cerebral artery peak systolic velocitiesTwin anemia-polycythemia sequence (TAPS)
  • Monochorionic gestation demonstrating one structurally normal fetus and an amorphous fetal mass receiving retrograde umbilical arterial flowTwin reversed arterial perfusion (TRAP) sequence
  • Monochorionic monoamniotic gestation presenting with sudden-onset, simultaneous profound bradycardia in both fetusesUmbilical cord entanglement

Answer

The correct matches are: 1) Fluid volume discordance matches with TTTS. 2) MCA-PSV discordance matches with TAPS. 3) Acardiac mass with retrograde flow matches with TRAP sequence. 4) Sudden bradycardia in a monoamniotic gestation matches with umbilical cord entanglement.
Monochorionic twin gestations are at high risk for unique complications due to shared placental vascular anastomoses. TTTS presents with severe amniotic fluid discordance (oligohydramnios/polyhydramnios). TAPS presents with anemia/polycythemia discordance (measured by abnormal MCA-PSV) but maintains normal fluid volumes. TRAP sequence involves a structurally normal twin perfusing an anomalous, acardiac mass via retrograde flow. Monoamniotic twins, lacking a dividing membrane, are uniquely susceptible to cord entanglement, causing acute fetal distress such as bradycardia.

Step-by-Step Solution

1
Evaluate the amniotic fluid volumes in the diamniotic gestation.
Discordant amniotic fluid (polyhydramnios/oligohydramnios sequence) points to TTTS.
Large arteriovenous anastomoses cause rapid volume shifts and renal perfusion disparity between the twins.
2
Assess for fetal anemia markers when fluid volumes are normal.
Discordant MCA-PSV without fluid discordance points to TAPS.
Microscopic anastomoses cause slow red blood cell transfusion, leading to anemia/polycythemia without massive fluid volume shifts.
3
Identify structural anomalies and flow direction in a monochorionic pair.
An acardiac mass with retrograde umbilical flow is pathognomonic for TRAP sequence.
Arterio-arterial anastomoses allow the pump twin to perfuse the acardiac twin backward, preventing normal cardiac development.
4
Consider the chorionicity and amnionicity of the pregnancy in the setting of acute fetal compromise.
Sudden bradycardia in a monoamniotic gestation is most commonly due to cord entanglement.
The lack of an intertwin membrane allows the umbilical cords to freely cross, twist, and acutely compress.

Key Concept

Diagnosis of monochorionic multifetal gestation complications
Estimated Time:1m 30s
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Topics

Obstetric Complications

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