Twin-to-twin transfusion syndrome (TTTS)

TTTS only occurs in monozygotic (identical) twins with a monochorionic placenta. It is the result of an intrauterine blood transfusion from one twin (donor) to another twin (recipient). The donor twin is often smaller with a birth weight 20% less than the recipient’s birth weight. The donor twin is often anemic and the recipient twin is often plethoric with hemoglobin differences greater than 5 gm/dL. The blood transfusion from the donor twin to the recipient twin occurs through placental vascular anastomoses. The most common vascular anastomosis is a deep, artery-to-vein anastomosis through a shared placental cotyledon.