What is essential for the diagnosis of Twin-Twin Transfusion Syndrome (TTTS)?

The essential criterion for diagnosing Twin-Twin Transfusion Syndrome (TTTS) is the presence of both polyhydramnios and oligohydramnios. TTTS occurs in monochorionic twin pregnancies, where blood flow between the twins is imbalanced due to anastomoses in the shared placenta.

In this condition, one twin (the donor) receives less blood flow, leading to oligohydramnios, which is a decrease in amniotic fluid surrounding the donor twin. Conversely, the other twin (the recipient) receives an excess blood flow, resulting in polyhydramnios, which is an accumulation of excess amniotic fluid around the recipient twin. The hallmark of TTTS is this disparity in amniotic fluid levels between the twins, making the combination of oligohydramnios and polyhydramnios crucial for diagnosis.

Diagnosing TTTS requires recognizing this fluid imbalance rather than identifying each condition individually. While intrauterine growth restriction may be observed in one or both twins, it is not a definitive criterion for diagnosing TTTS on its own. Having both types of amniotic fluid levels is indicative of the underlying pathophysiology specific to TTTS.