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Twin-to-twin transfusion syndrome

What is twin-to-twin transfusion syndrome?

Twin-to-twin transfusion syndrome (TTTS) is a disease of the placenta. It develops in identical twins during pregnancy, when a disproportionate amount of blood passes through the connecting blood vessels in the shared placenta from one twin to the other. One fetus (the recipient) acquires too much blood, which causes stress on the cardiovascular system and may lead to death from heart failure. The other twin (the donor) retains too little blood and may die from the undersupply. 

The recipient produces excessive amounts of urine and amniotic fluid, which causes discomfort to the mother and results in pressure on the cervix. With continuing pressure the cervix may open, resulting in miscarriage or preterm delivery. The donor twin produces hardly any urine and therefore has almost no amniotic fluid in his amniotic sac. 

In most cases of twin-to-twin transfusion syndrome, the twins themselves are completely healthy. The problem which frequently results in malformations of the twins lies in the placenta. 

What causes twin-to-twin transfusion syndrome?

Twin-to-twin transfusion syndrome only affects identical twins who share a single placenta. It is believed that TTTS is initiated when cleavage of the fertilized egg occurs and the structure of the placenta and vessel connections is determined. 

TTTS and other problems are more severe the later the cleavage of the fertilized egg takes place. Almost all cases of TTTS are found in identical twins with separate amniotic sacs and a single placenta. 

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