Ultrasound in a twin pregnancy at 18 weeks shows both fetuses in a single chorionic sac (monochorionic) with discordant amniotic fluid (one polyhydramnios, one oligohydramnios) and a stuck twin. What condition does this describe?
- A Twin reversed arterial perfusion (TRAP) sequence
- B Twin-to-twin transfusion syndrome (TTTS) ✓
- C Selective intrauterine growth restriction (sIUGR)
- D Discordant fetal anomaly
Correct answer: B. Twin-to-twin transfusion syndrome (TTTS)
Explanation
Twin-to-twin transfusion syndrome (TTTS) is a serious complication of monochorionic-diamniotic (MCDA) twins due to unbalanced placental arteriovenous anastomoses. The donor twin develops oligohydramnios and appears stuck against the uterine wall (stuck twin), while the recipient develops polyhydramnios and may develop hydrops from volume overload. Staging by Quintero criteria guides fetoscopic laser ablation therapy. TRAP sequence shows acardiac twin. sIUGR shows growth discordance without the fluid discordance pattern.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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