What is a primary pathological mechanism of Twin-Twin Transfusion Syndrome (TTTS)?

Twin-Twin Transfusion Syndrome (TTTS) primarily involves an imbalanced blood flow between the two fetuses due to shared placental circulation. In this condition, one fetus, known as the donor, experiences a decrease in blood volume, while the other fetus, the recipient, receives an excess of blood. This net transfusion effect occurs due to the presence of abnormal connections between the vessels in the placenta.

In the context of TTTS, the donor twin is at risk for anemia and growth restriction because it is essentially "giving" blood to the recipient twin, resulting in a transfusion effect. This imbalance can lead to significant complications, including heart failure in the recipient twin and poor development in the donor twin.

While hypervascularization refers to an increase in blood vessels and could be seen in some placental abnormalities, it does not specifically explain the primary mechanism of TTTS. Similarly, bidirectional blood flow can occur in different scenarios but is not the main pathological mechanism that defines TTTS. Placental detachment, or abruption, is a separate complication and does not occur as a feature of this syndrome. Thus, the net transfusion from donor to recipient accurately captures the essence of what happens in TTTS, illustrating the abnormal inter-t