Chorionicity drives twin complications, so anchor on the membranes. In an MCDA gestation there is one placenta shared by both fetuses but a two-layer dividing membrane creates two distinct amniotic compartments.
Shared-placenta problems still apply: unequal placental sharing produces selective FGR, the anastomoses can cause TTTS/TAPS, and monochorionic twins carry an excess of structural anomalies and deformities. So options offering sFGR and deformities are genuine MCDA risks.
The trap option is cord entanglement. Two cords can only knot around each other when both fetuses float in the same sac. That situation is monoamniotic (MCMA), where there is no separating membrane. The diamniotic membrane in MCDA keeps each cord in its own sac, so entanglement is essentially excluded.
First-trimester MTP is an elective intervention and not a disease complication, but the single best discriminator the examiner wants is the membrane-dependent event.
\[\boxed{\text{Cord entanglement — an MCMA, not MCDA, complication}}\]