Twin-to-Twin Transfusion Syndrome (TTTS) is a severe complication occurring in monochorionic (identical) twin pregnancies. If left untreated, the mortality is very high and fetuses will die in utero or after birth in most cases. Early diagnosis and treatment are essential for improving the poor prognosis of these pregnancies. There are at present mainly two established options for the treatment of the syndrome, but it is not clearly established which is the best, which raises the need for further evaluation.

What is Twin-to-Twin Transfusion Syndrome
TTTS occurs in 10% to 15% of identical twins. One fetus is passing blood to the other over abnormal connecting vessels in their shared placenta. These connections are normally existing in most identical twins but, in a small proportion of these pregnancies, and due to unknown reasons, connecting vessels lead to TTS. Therefore, the fetuses are normal but there is a problem in the placenta.

Consequences of TTTS
In advanced cases the fetus who is transfusing (the donor) does not get enough blood and develops severe anemia, and the transfused fetus (the recipient) gets too much blood and its heart must work over its capacity, which eventually leads to heart failure. The prognosis for both fetuses is extremely poor, and the mortality in utero ranges from 60% to 100%, with almost one third of survivors presenting with severe complications after birth.

Diagnosis of TTTS
The TTS is detected by ultrasound examination. The donor fetus is frequently smaller in size than the recipient and there is very little fluid in its amniotic sac. The recipient fetus is usually larger and passing more urine, which causes an excessive amount of fluid in its amniotic sac.

Treatment options for TTTS

• Serial amniodrainage consists in performing amniocentesis (inserting a needle into the gestational sac), once or as frequently as required, to eliminate excessive fluid. The average survival achieved by amniodrainge is about 60 %, but neurodevelopmental impairment has been described to be around 20% of surviving infants.
• A more recent development is fetoscopic laser surgery. Direct vision of the placenta is achieved through an endoscope, and the communicating vessels are identified and destroyed with a laser. Experience with over 300 cases gives a survival rate of 55 % to 60 %, with at least one survivor in 75-80 % of pregnancies. Neurological damage in surviving infants at one year of age is around 5 %.

The Eurofoetus programme is conducting two main activities in the field of TTS open to participation of all centers preferentially via the Internet:

The Twin-Twin Transfusion Syndrome Randomized Trial
Observational Study on TTS