What is Twin-To-Twin Transfusion Syndrome?

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  • Written By: Lisa Weber
  • Edited By: Angela B.
  • Last Modified Date: 08 October 2019
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Twin-to-twin transfusion syndrome is a problem that affects unborn identical twins as a result of a problem with the placenta. In normal twin pregnancies, the two fetuses are able to share the placenta, the organ that helps feed the growing fetus via the mother's blood supply. In most cases of twin-to-twin transfusion syndrome, one twin gets most of the placenta's flow of blood, while the other twin gets far less than its share. Although at one time the results were devastating to the mother and her family, advances in obstetrics now allow most twins to survive this condition.

TTTS is a random occurrence, affecting approximately 15 percent of identical twin pregnancies. Each fetus in a set of fraternal twins has his or her own placenta, so this condition is not an issue for fraternal twins. Twin-to-twin transfusion syndrome is not a birth defect; it is not a matter of hereditary — genetics do not play a role — and it's not the result of the parents' actions or inactions.

In twin-to-twin transfusion syndrome, each twin tries to adapt to its situation. The twin who is not receiving the blood flow tries to conserve water and energy. This causes a condition called oligohydramios, or low amniotic fluid volume. The other twin, the one receiving more than its share of blood, tries to get rid of the increased fluid through increased urination, a condition known as polyhydramnios.


A mother whose pregnancy is affected by twin-to-twin transfusion syndrome may see sudden growth in her womb. Her uterus may measure large for her expected due date, she may gain weight much more quickly than common, and her hands or legs may swell early in her pregnancy. A doctor looking at an ultrasound may see evidence of a shared placenta.

There are two types of twin-to-twin transfusion syndrome — acute and chronic. Chronic TTTS is more common, and happens gradually; it is often diagnosed during a routine ultrasound. If this happens, the doctor will usually prescribe bed rest and a nutrition program for the mother. Acute TTTS happens without warning after the 30th week of pregnancy. It may also happen during a vaginal delivery, or after the cord of one twin has been clamped.

Until recently, TTTS would often claim the lives of both twins, but there are now two treatments available. Amniocentesis may be used to drain excess fluid, which improves the blood flow in the placenta and reduces the risk of preterm labor. This method can prevent fatalities about 60 percent of the time. Laser surgery may be used in extreme cases. If the babies are mature enough to survive on their own, a doctor may choose to deliver them early.

Less-than-ideal conditions in the womb mean babies affected by twin-to-twin transfusion syndrome may have lingering health problems. The twin who received too much blood may have respiratory, digestive, or heart defects as a result of the excess fluids; the twin who received too little blood may develop anemia. If the twins are delivered prematurely, there also may be developmental delays.


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