Twin-to-twin transfusion syndrome (TTTS) is a rare condition that occurs only in identical twins while they are in the womb.

TTTS occurs when blood moves from one twin to the other. The twin that loses the blood is called the donor twin. The twin that receives the blood is called the recipient twin.

Both infants may have problems depending on the severity of the transfusion. The donor twin may have too little blood, and the other may have too much blood. The donor twin may need a blood transfusion, while the recipient twin may need to have the amount of blood in his or her body reduced.

The donor twin is usually born smaller that the other twin, usually with paleness, anemia, and dehydration.

The recipient twin is born larger, with redness, too much blood, and increased blood pressure. Because of the increased blood volume, the recipient twin may develop cardiac failure and also require medications to strengthen heart function.

The unequal size of identical twins is referred to as discordant twins.

This condition is usually diagnosed by ultrasound during pregnancy.

After birth, the infants will receive the following tests:

• Blood clotting studies, including prothrombin time (PT) and partial thromboplastin time (PTT)
• Chem-20 to determine electrolyte balance
• Complete blood count
• Chest x-ray

Treatment may require repeated amniocentesis during pregnancy. Fetal laser surgery may be done to interrupt the flow of blood from one twin to the other.

After birth, treatment depends on the infant's specific symptoms. The donor twin may need a blood transfusion to treat anemia.

The recipient twin may need to have the volume of body fluid reduced. This may involve an exchange transfusion.

Medications may be given to treat heart failure in the recipient twin.

If the twin-to-twin transfusion is mild, full recovery is expected for both babies. However, severe cases may result in the death of a twin.