Twin-to-twin transfusion disorder (TTTS) is an uncommon pregnancy condition that affects identical twins or other multiple pregnancies. TTTS happens in pregnancies where twins share one placenta (fetal membrane) and blood vessels that supply oxygen and nutrients that are important for growth. These pregnancies are termed as monochorionic.
There are some cases when the blood vessels inside the placenta are not uniformly apportioned and there is an imbalance in the circulation between the twins. One twin, the giver twin, parts gives more blood than it gets consequently and develops malnourishment and organ problems. The beneficiary twin gets an excess of blood and is vulnerable to heart failure and other cardiovascular problems.
TTTS can happen during pregnancy, even when a mother is in the process of giving birth at term. The placental problems cause a transfusion to happen between the twins.