What is Twin-Twin Transfusion Syndrome

Twin-Twin Transfusion Syndrome (TTTS) is a rare, serious condition occurring in identical twin pregnancies sharing a single placenta where blood flows disproportionately from one twin to the other. This imbalance causes the "donor" twin to become dehydrated and growth-restricted, while the "recipient" twin faces fluid overload and cardiac strain, necessitating specialized fetal intervention.

What causes Twin-Twin Transfusion Syndrome?

Twin-Twin Transfusion Syndrome occurs due to abnormal vascular connections (anastomoses) within the shared placenta. In a healthy monochorionic pregnancy, blood exchange is usually balanced. In Twin-Twin Transfusion Syndrome, these connections allow blood to flow predominantly in one direction. This leads to the donor twin having decreased amniotic fluid (oligohydramnios) and the recipient twin having excessive amniotic fluid (polyhydramnios), which can trigger preterm labor or cardiac failure.

How common is Twin-Twin Transfusion Syndrome?

Twin-Twin Transfusion Syndrome affects approximately 10% to 15% of all identical (monochorionic) twin pregnancies. Because it is specific to pregnancies where twins share a placenta, it is not linked to gender or geographic factors, but rather the unique vascular anatomy of the placenta. At DiseaseMaps.org, 9 people have joined our community to share their experiences with this challenging diagnosis.

How is the severity classified?

Physicians typically use the Quintero staging system to assess the progression of Twin-Twin Transfusion Syndrome:

• Stage I: Discrepancy in amniotic fluid volume.


• Stage II: The donor twin’s bladder is not visible on ultrasound.


• Stage III: Abnormal blood flow patterns in the umbilical cord or heart.


• Stage IV: Signs of heart failure (hydrops) in the recipient twin.


• Stage V: Demise of one or both twins.

What differentiates this from other twin complications?

Unlike Selective Intrauterine Growth Restriction (sIUGR), which is primarily a placental insufficiency issue, Twin-Twin Transfusion Syndrome is characterized by the active shunting of blood volume. This makes Twin-Twin Transfusion Syndrome a hemodynamic emergency that often requires rapid evaluation by a fetal medicine specialist.

Next steps

• Consult a Maternal-Fetal Medicine (MFM) specialist immediately if a monochorionic pregnancy is confirmed.


• Request serial ultrasound monitoring every 1–2 weeks starting at 16 weeks gestation.


• Connect with the community at DiseaseMaps.org to find support from others who have navigated a Twin-Twin Transfusion Syndrome diagnosis.

Medical disclaimer: This information is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Twin-Twin Transfusion Syndrome overview.


• Orphanet: Rare disease database entry for Twin-Twin Transfusion Syndrome.


• The Fetal Health Foundation: Patient resources and clinical information on TTTS.


• PubMed: Clinical guidelines on the management of monochorionic twin pregnancies.