What is twin-to-twin transfusion syndrome (TTTS)?

Twin-to-twin transfusion syndrome (TTTS) is a condition that occurs in about 10-15% of identical twins that share a placenta. When twins form from one egg and one sperm and divide at the appropriate time in gestation, they’re in separate amniotic sacs, but have one placenta where they share a blood supply. Most of the time, this is a balanced communication between the twins. But in 10-15% of identical twin pregnancies, that communication becomes unbalanced, and one baby will actually donate blood to the other baby. When this happens, the baby that is donating the blood becomes dehydrated, stops making urine and we see a decrease in amniotic fluid volume. For the baby that’s receiving the extra blood, we will see a volume-overload condition where the baby makes a lot of extra urine and has extra amniotic fluid. This condition can proceed to heart failure. TTTS can be fatal for both babies if it’s not treated to stop the transfusion.

What patients are at risk for developing TTTS?

Patients that are at risk of developing twin-to-twin transfusion syndrome are patients with twins that share a placenta. Twins with separate placentas, which are actually the majority of twins, will not develop twin-to-twin transfusion syndrome.

What causes TTTS?

The cause of twin-to-twin transfusion syndrome isn’t fully understood. The placenta is a very dynamic organ during gestation, and as the different portions of the placenta grow and enlarge to help enhance blood supply to the babies, it’s assumed that those vascular communications can sometimes become unbalanced. This condition can occur very rapidly, which is why frequent ultrasounds are recommended.

How is TTTS diagnosed?

Twin-to-twin transfusion syndrome is diagnosed by ultrasound, and is evident when one child has extra amniotic fluid and the other is showing a significant decrease in amniotic fluid. The mother may also feel a rapid enlargement of her uterus, more quickly than is expected during pregnancy. There may also be abnormalities in the blood flow patterns in the umbilical cord.

Patients with identical twins that share a placenta should undergo frequent ultrasounds to evaluate amniotic fluid volumes. Typically ultrasounds are performed every 2 weeks starting at 16 weeks. The frequency of ultrasounds increases in the third trimester. If there is any fluid discrepancy or other concerning findings, then those patients will need further evaluation immediately. Additionally, we will have a pediatric cardiologist perform an ultrasound of the heart (fetal echocardiogram) to assess the heart structure and function.

How is it treated?

The key to treating twin-to-twin transfusion syndrome is early diagnosis and intervention. Depending on the stage of TTTS and the gestational age at diagnosis, treatment options include:

  • Expectant management – this would involve continued close ultrasound surveillance
  • Amnioreduction – a needle procedure where the excess amniotic fluid is removed from the twin with too much volume (recipient twin). Oftentimes, amnioreduction needs to be repeated if the fluid reaccumulates.
  • Fetoscopic laser photocoagulation – A minimally invasive surgery that ablates the vessels that are shared between the donor and the recipient. In general, this treatment has improved outcomes for the pregnancy.
  • Selective cord occlusion – A procedure that stops the blood flow in the umbilical cord of one twin in order to optimize the outcome for the other twin.
  • Delivery – if TTTS is discovered late in pregnancy, delivery may be the best option.

What is the long-term prognosis?

If left untreated, the long-term prognosis for twin-to-twin transfusion syndrome is very poor, and often greater than 90% of the fetuses won’t survive to birth. After fetal surgery and laser ablation on the placental vessels, approximately 85% of patients will have at least one surviving fetus that will be healthy at discharge from the NICU. Survivability of both twins still remains a problem and is approximately 40% across all centers, internationally.


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Midwest Fetal Care Center is a collaboration between Children’s Minnesota and Allina Health.