THE ETIOLOGY OF CHRONIC TWIN-TO-TWIN TRANSFUSION SYNDROME

• A. Is based on the dizygotic nature of the conceptuses
• B. Is undoubtedly due to the associated reversed arterial perfusion sequence in the acardiac twin
• C. Produces hypovolemia and anemia in the recipient and hypervolemia and polycythemia in the donor
• D. Is based on unbalanced arterial to venous anastomotic connections between the twins in the placenta ✓

Twin-to-twin transfusion syndrome (TTTS) is a serious condition that can occur in pregnancies where identical twins share a placenta. In TTTS, there are abnormal connections between the blood vessels of the twins in the placenta, leading to an imbalance in the blood flow between them. This results in one twin (the donor) receiving too little blood and nutrients while the other twin (the recipient) receives too much.

The etiology of chronic TTTS is primarily attributed to unbalanced arterial to venous anastomotic connections between the twins in the placenta. These abnormal connections lead to an unequal distribution of blood flow, causing hypovolemia and anemia in the recipient twin and hypervolemia and polycythemia in the donor twin.

In other words, Chronic twin-to-twin transfusion syndrome is a condition that occurs in monochorionic diamniotic twin pregnancies where there is an imbalance in blood flow between the twins sharing the same placenta. The correct statement regarding the etiology of chronic twin-to-twin transfusion syndrome is:

D. Is based on unbalanced arterial to venous anastomotic connections between the twins in the placenta

This statement accurately reflects the underlying cause of chronic twin-to-twin transfusion syndrome, which is primarily attributed to abnormal vascular connections within the shared placenta leading to imbalanced blood flow between the twins.

In contrast, option A is incorrect as TTTS can occur in both monozygotic (identical) and dizygotic (fraternal) twins, not solely based on their zygosity. Option B refers to another condition called acardiac twinning or TRAP sequence, which is different from TTTS. Option C describes the consequences of TTTS rather than its etiology.