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Colorado Fetal Care Center

Twin-to-Twin Transfusion Syndrome (TTTS)

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

Twin-to-twin transfusion syndrome (TTTS) is a disorder that affects identical twin pregnancies. It can occur when two fetuses share a placenta (referred to as a monochorionic twin pregnancy) because there isn’t a barrier separating the two fetuses from each other.

Sometimes, blood vessels from the twins' umbilical cords form abnormal connections within their shared space, connecting one baby to the other. When this happens, blood flows unevenly between the babies and their circulations become unbalanced. This puts the twins at risk for early delivery, neurological damage and more.

Twin-to-twin transfusion syndrome (TTTS) is a serious, rare condition only seen in identical twins who share a placenta (monochorionic).

One fetus (called the "donor" twin) "donates" their circulation of fluid and blood to the other fetus (known as the "recipient"). As a result, the donor twin may stop producing urine and its amniotic sac becomes much smaller.

The recipient twin receives too much blood and urine and produces more amniotic fluid, resulting in having a very large amniotic sac.

TTTS can lead to severe complications for the twins. That's why early detection is critical to help improve outcomes for both babies and their mother.

What causes TTTS in pregnancy?

The exact cause of TTTS is not well understood; there are no known genetic causes of TTTS, and there's nothing a mother did to cause it. In the majority of cases, TTTS develops in the second trimester of pregnancy.

While there's nothing anyone can do to prevent TTTS, there's plenty we can do to help your babies. The important thing that families can do when they are diagnosed with monochorionic-diamniotic twins is to have close and early surveillance for TTTS, specifically by having ultrasounds every two weeks starting at 16 weeks of gestation.

Who gets TTTS?

TTTS can affect identical twins before they are born. Approximately 1 in every 250 pregnancies are identical or monochorionic and approximately 2 out of 3 of these pregnancies are monochorionic diamniotic, meaning the fetuses share a placenta but have two separate amniotic sacs. Of these pregnancies, 10% to 15% develop TTTS.

Although less common, TTTS can happen in monochorionic monoamniotic twins where the twins are in one sac without a dividing membrane.

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Adel Younoszai, MD

Adel Younoszai, MD

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