Prenatal Medicine

Twin to Twin Transfusion Syndrome

Twin to Twin transfusion syndrome (TTTS) is a disease of the placenta. It develops in identical twins during pregnancy because of the presence of connecting blood vessels between the two umbilical cords. There is repeated transfusion of small amounts of blood between the two twins through these vascular connections.

Where detected, TTTS is commonly treated by Serial Amnioreduction (drainage of amniotic fluid). This treatment reduces the risk of premature delivery and in about 20% of the cases TTTS stops. However, in most cases the effects on TTTS on the foetuses remain unchanged.

Advantages of laser therapy for TTTS

The receiving foetus (the recipient) has too much blood volume, which can result in heart failure and death in the womb. The transfusing twin (the donor) has too little blood volume and may die due to malnutrition.

This form of therapy attempts the treatment of the underlying cause for TTTS by using the laser to occlude the connecting vessels, therefore stopping the blood flow between the donor and the recipient. Then an amnioreduction is performed.

The advantage of this form of therapy is that it aims at the underlying cause of TTTS and that following the closure of all connecting vessels the twins have a significantly higher chance for subsequent normal development. However laser therapy for TTTS is not yet widely available.

The disadvantage lies in the miscarriage risk associated with amnioreduction and the fact that the issue of Twin to Twin transfusion is not addressed.

NOTE: The following text is provided courtesy of the University Medical Centre, Hamburg-Eppendorf, Germany

What Causes Twin to Twin Transfusion Syndrome?

The Twin to Twin transfusion syndrome only affects identical twins who share a single placenta. It is believed that the basis for the development of TTTS is initiated at the time when cleavage of the fertilised egg begins and the structure of the placenta and vessel connections are determined.

It is known that problems including TTTS are more severe if the cleavage of the fertilised egg occurs later. Nearly all cases of TTTS are found in identical twins with separate amniotic sacs and a single placenta.

Standard treatment: Serial amnioreduction (drainage of amniotic fluid)

During the procedure amniotic fluid is drained through a needle which is inserted into the amniotic sac of the recipient through the wall of the uterus. This treatment reduces the risk of premature delivery and in about 20% of the cases TTTS stops. However, in most cases the effects on TTTS on the foetuses remain unchanged.

The advantage of this form of treatment is that it can be performed at many centres. The disadvantages lie in the miscarriage risk associated with amnioreduction and the fact that the issue of Twin to Twin transfusion is not addressed.

It is estimated that 15% of identical twin pregnancies with a single placenta, or one in 2700 pregnancies develop twin to twin transfusion syndrome.

However, the true incidence may be higher since many patients with TTTS who have spontaneous miscarriage may not be reported.

How common is TTTS?

Visit the Obstetrics Centres page for details of centres offering Laser TTTS and other treatments.

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