What ultrasound findings define Stage III Twin-to-Twin Transfusion Syndrome (TTTS)?

Stage III Twin-to-Twin Transfusion Syndrome (TTTS) is characterized by significant and potentially life-threatening imbalances in blood flow between the twins. The correct answer focuses on the combination of pulsatile flow in the umbilical vein and abnormal Doppler findings in the umbilical artery, specifically absent or reversed end-diastolic flow (AEDF/REDF).

This combination indicates severe hemodynamic compromise, where one twin (the donor) is losing blood flow and experiences a poor perfusion state, while the other twin (the recipient) is receiving excessive blood flow, leading to increased blood volume. The pulsatile flow in the umbilical vein is a response to the increased pressure and can signify heart strain in the recipient twin, while the abnormal flow patterns in the umbilical artery reflect the severe vascular changes occurring as a result of the TTTS pathology.

Recognizing these ultrasound findings is crucial in diagnosing Stage III TTTS, as they guide clinical management decisions, such as potential interventions to improve outcomes for both twins.