Twin-Twin Transfusion Syndrome (TTTS)

What is TTTS?

Twin-twin transfusion syndrome (TTTS) is a problem where one fetus — the donor twin — pumps blood to the other fetus — the recipient twin. The condition occurs in about 10 percent of all pregnancies where identical twins share a placenta. That amounts to about 2,000 patients per year in the U.S.

Without intervention, the recipient twin receives too much blood and may develop fluid overload, heart failure, and die, and the donor twin may die from not having enough blood (severe anemia).

Almost all identical twins exchange blood across the placenta, although usually the exchange is balanced. In TTTS, the blood connections in the placenta are abnormal and the blood passes unequally between the two fetuses. TTTS occurs in varying stages of severity, which may or may not progress to the point where intervention is needed.

What causes TTTS?

The exact cause of TTTS is unknown. There are several variations of blood vessel development that may lead to unbalanced blood exchange. In addition, the fetus's response to altered blood volume may worsen the condition.

What are the symptoms of TTTS?

Symptoms of the recipient twin:

  • very large amount of urine in the bladder
  • too much amniotic fluid in the sac (polyhydramnios)
  • larger than the donor twin and possibly swollen with too much blood
  • congenital heart failure from an excess of blood

Symptoms of the donor twin:

  • little or no urine in the bladder
  • too little amniotic fluid in the sac (oligohydramnios)
  • much smaller than the recipient twin

How we care for TTTS

Through the joint work of researchers, genetic specialists, surgeons, and other care providers, the Boston Children's Hospital Maternal Fetal Care Center is breaking ground in understanding and successfully treating a wide variety of fetal health concerns, including TTTS.