Final answer:
The plethoric infant in TTTS is likely to encounter Polycythemia as a primary complication, due to the excess number of red blood cells leading to thickened blood and related health issues.
Step-by-step explanation:
In the case of Twin-Twin Transfusion Syndrome (TTTS), a condition where one twin receives more blood flow than the other due to abnormal connecting blood vessels in the shared placenta, the most likely complication for the plethoric infant (one who is ruddy in complexion or swollen with blood) is Polycythemia. This is where there is an abnormally high number of red blood cells that can lead to an increased risk of blood clots, strokes, and decreased blood flow due to the thickened blood. Other potential complications for the plethoric twin may include anemia, edema, enlarged liver or spleen, and hydrops (fluid in body cavity), which can be severe and even lead to the death of the newborn in extreme cases.