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What is Twin-Twin Transfusion Syndrome & How is it Treated?

What is Twin-Twin Transfusion Syndrome?

Twin-Twin Transfusion Syndrome is an extremely rare pathological condition which tends to occur when females are pregnant with monozygotic or identical twins. Twin-Twin Transfusion Syndrome stems from the placenta which is the organ which connects the mother to the unborn baby and functions by providing nourishment to the fetus.

In cases of identical or monozygotic twins the placenta is shared between the two fetuses which results sometimes in sharing of the blood vessels resulting in a connection of the blood circulation.

In majority of the cases the blood flows normally in both the fetuses but in cases of Twin-Twin Transfusion Syndrome there is uneven blood flow with one fetus receiving more blood than the other twin. This may result in the heart of the twin receiving less blood getting affected as a result of too much strain being put on it due to excessive blood supply whereas the other twin which receives less blood may suffer from severe anemia due to lack of oxygen and insufficient blood supply. The nutrition for this twin also gets affected.

This imbalance of blood flow to the twins may occur at anytime during the pregnancy and in some cases at the time of delivery also causing Twin-Twin Transfusion Syndrome.

The severity of the symptoms of Twin-Twin Transfusion Syndrome depends on which stage of pregnancy does the abnormality in blood circulation occurs, its diagnosis, and when the treatment for it actually starts. What exactly causes this abnormality in blood circulation is not well known in cases of Twin-Twin Transfusion Syndrome.

What is Twin-Twin Transfusion Syndrome?

What are the Causes of Twin-Twin Transfusion Syndrome?

As stated, the root cause for Twin-Twin Transfusion Syndrome is not yet known. Some studies suggest that some type of abnormalities during division of the fertilized egg of the mother may cause placental abnormalities which may result in development of Twin-Twin Transfusion Syndrome.

Under normal circumstances, the development of a monozygotic or identical twins starts with fertilization of the egg of the mother by the sperm of the father. Within a few days, the fertilized egg divides into two identical embryos which are nourished by their respective placentas which ultimately develop into two distinct individuals with more or less identical genetic makeup.

In some cases however it takes a longer time for the egg to divide into two embryos and studies suggest that the longer it takes for the embryos to divide the more problems are likely to happen in the future with the pregnancy advancing and the more likelihood for development of Twin-Twin Transfusion Syndrome.

What are the Symptoms of Twin-Twin Transfusion Syndrome?

In most of the cases of pregnancy with monozygotic twins, the placenta is shared by both the twins with a common umbilical cord and blood circulation. The twins are joined together to the placenta by the umbilical cords.

Under normal circumstances the blood flow to both the twins is even but in cases of Twin-Twin Transfusion Syndrome this blood circulation is uneven with one twin receiving more blood than the other resulting in a variety of symptoms which vary depending on the stage of pregnancy when this abnormality started to occur.

The abnormality causing Twin-Twin Transfusion Syndrome may occur at any time during the pregnancy but if it occurs within the first trimester then one of the fetus may stop growing with the result being that only one fetus will be observed for the remainder of the pregnancy.

If this condition occurs at the time of delivery or shortly before delivery the symptoms displayed by the twins may resemble that of symptoms caused by sudden lack of blood supply or excessive blood supply to the body.

If Twin-Twin Transfusion Syndrome occurs midterm then a variety of symptoms may occur to include increased urinary output from the twin receiving excess blood causing an increase in the amniotic fluid. This increase in amniotic fluid may cause the abdomen of the mother to bulge out more than normally during that stage of pregnancy. For majority of the cases, this is the first symptom of Twin-Twin Transfusion Syndrome. This increase in amniotic fluid may cause preterm labor and early delivery.

For the other twin, which receives very less supply of blood the kidneys of the fetus may stop developing enough urine resulting in decreased amniotic fluid. This may result in the membranes of the amniotic sac to collapse and the second twin may look like it is stuck within these collapsed membranes

How is Twin-Twin Transfusion Syndrome Diagnosed?

Twin-Twin Transfusion Syndrome is usually detected during the second trimester of the pregnancy via an ultrasound which will show a shared placenta, extremely thin membrane which divides the fetuses’ amniotic sacs, abnormality in the amount of amniotic fluid present with either excess amniotic fluid or extremely less amniotic fluid.

Once the babies are delivered examination of the placenta can confirm the presence of connecting blood vessels and the symptoms that the babies will exhibit will confirm the diagnosis of Twin-Twin Transfusion Syndrome.

How is Twin-Twin Transfusion Syndrome Treated?

If the diagnosis of Twin-Twin Transfusion Syndrome is made before delivery then there are surgical tool which are available which can be used to view the placenta and can be utilized to obstruct the connecting blood vessels via laser and thus separate the blood flow and making it more even and treating Twin-Twin Transfusion Syndrome.


  1. Mayo Clinic. (2021). Twin-Twin Transfusion Syndrome. https://www.mayoclinic.org/diseases-conditions/twin-twin-transfusion-syndrome/symptoms-causes/syc-20420578
  2. American Pregnancy Association. (2021). Twin to Twin Transfusion Syndrome (TTTS). https://americanpregnancy.org/multiples/twin-to-twin-transfusion-syndrome/
  3. The Fetal Health Foundation. (n.d.). Twin to Twin Transfusion Syndrome. https://www.fetalhealthfoundation.org/conditions/twin-to-twin-transfusion-syndrome-ttts/
Pramod Kerkar, M.D., FFARCSI, DA
Pramod Kerkar, M.D., FFARCSI, DA
Written, Edited or Reviewed By: Pramod Kerkar, M.D., FFARCSI, DA Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:August 3, 2023

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