What is twin-to-twin transfusion?

Twin-to-twin transfusion is a condition that can develop in two or more fetuses who share the same placenta. In this condition, abnormal blood vessels develop in the placenta and move blood from one twin to another. The risks of twin-to-twin transfusion include stillbirth of one or both twins or severe complications in one or both twins after birth. When blood shifts from one fetus (the donor) through the placenta to the other fetus (the recipient), the donor twin may:

• Be smaller.
• Not have enough red blood cells (anemia).
• Be surrounded by less amniotic fluid.
• Develop heart failure after birth. The recipient twin may:
• Be larger.
• Have too many red blood cells.
• Be surrounded by too much amniotic fluid.
• Develop heart failure after birth.
• Develop too much bile in the blood (referred to as hyperbilirubinemia or jaundice). Bile comes from the breakdown of excess red blood cells.

Twin-to-twin transfusion is suspected when a fetal ultrasound shows that one twin is much larger than the other. Treatment can include amniocentesis to remove excess amniotic fluid. After birth, the donor twin may require a blood transfusion while the recipient twin may need to have some blood removed. Both twins may need treatment for heart failure.

Twin to twin transfusion syndrome (TTTS) is an abnormality of the placental vasculature during pregnancy which affects identical twins. Identical twins share a common monochorionic placenta. If the placenta contains abnormal blood vessels the umbilical cord blood flow and the circulations of the fetuses becomes connected. As a result one fetus, known as the donor, receives less blood flow and the nutrients it contains which the other fetus, known as the recipient, receives more blood flow and the nutrients it contains.

At birth, both infants may have problems depending on the severity of the transfusion syndrome. The donor twin may have too little blood and need a blood transfusion, while the recipient twin may have too much blood and may need to have the amount of blood in his or her body reduced. While the infants are identical twins, they may have significantly different birth weight as the donor is frequently small from gestational age due to the lack of nutrients during intrauterine life which the recipient is bigger as a result of the increased volume of blood in the circulatory system.