Risks and Treatments of Twin to Twin Transfusion Syndrome (TTTS)

Twins sleeping in the hospital.
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Twin-to-twin transfusion syndrome is a condition of the placenta that affects some identical twin pregnancies. In TTTS, abnormal connections between the blood vessels in the placenta allow the blood from one twin to flow into the other twin. In some cases, twins share the common placenta unequally, and one twin may not have a share large enough to receive the necessary nutrients to grow normally or survive.

When Does TTTS Occur?

Twin-to-twin transfusion syndrome only happens when identical twins share a placenta.

TTTS can occur in triplet or higher pregnancies if two of the babies are identical and share a placenta.

Fraternal twins and identical twins with separate placentas are not at risk for TTTS.

What Are the Signs of TTTS?

TTTS twins have different symptoms based on whether they are donors or recipients.

Donor TTTS twins receive less blood from the placenta and lose blood to the other twin. Donor twins are smaller, both before and after birth. They are pale and anemic, have reduced urine output in utero, and smaller-than-average bladders. If the twins have two amniotic sacs, the donor twin will have reduced amniotic fluid (oligohydramnios).

Recipient twins receive too much blood, both from the placenta and from the other twin. These babies are larger and have excessive amniotic fluid (polyhydramnios). Because these babies have so much blood in their bodies, their circulatory systems may be overloaded, causing heart problems.

How Serious Is It?

Twin to twin transfusion syndrome may be fairly mild or very serious, depending on how unevenly blood is shared by the babies. Once TTTS is diagnosed, doctors will follow the pregnancy closely to see if the symptoms are progressing or not.

Stages of TTTS

  • Stage I: The donor twin has reduced amniotic fluid; the recipient twin has excessive amniotic fluid.
  • Stage II: Same as above. The donor twin’s bladder is not visible on an ultrasound — a sign of reduced urine output in utero.
  • Stage III: All of the above symptoms are present; blood flow in the umbilical cords is abnormal.
  • Stage IV: All of the above symptoms are present; the recipient twin is edematous and is showing signs of heart failure.
  • Stage V: All of the symptoms above are present and one twin has died.

How Is TTTS Treated?

When doctors realize that identical twins share a placenta, the mother will be closely followed for signs of TTTS.

If stage I TTTS is diagnosed, the mother will typically only be carefully monitored. Once TTTS progresses to stage II or III, doctors may try fetal laser surgery or amniotic fluid reduction.

Treatment may still be attempted later in the disease, but chances of success are lower.

In fetal laser surgery, laser therapy is used to separate blood vessels in the placenta that allow blood to flow from one twin to the other. The surgery is generally considered more successful than amniotic fluid reduction. Twins born after fetal laser surgery have a higher chance of survival and lower chance of having severe long-term effects of TTTS. The surgery does sometimes fail, however, and TTTS will continue to progress.

In serial amniotic fluid reduction, amniotic fluid is drained from the sac surrounding the recipient twin. The procedure may be done only once or several times. The theory behind amniotic fluid reduction is that reducing fluid reduces strain on the recipient twin’s heart and prevents preterm labor from occurring when excessive amniotic fluid places a strain on the cervix.

Long-Term Effects of TTTS

Many of the symptoms of mild TTTS, including anemia and polycythemia (a high red blood cell count), can be successfully treated after birth. Because many TTTS twin pregnancies do not go to term, the long-term effects of TTTS are similar to the long-term effects of prematurity.

In advanced cases of TTTS, the infants involved may have long-term effects beyond the problems of prematurity. Intraventricular hemorrhage and other brain lesions are more common in TTTS babies, even after laser treatment or amnioreduction. If the disease is untreated and not followed closely, long-term effects may include heart failure and death of one or both twins.

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