Twin-Twin Transfusion Syndrome (TTTS) Symptoms & Causes

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In-Depth

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.

How often does TTTS occur?

TTTS 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 United States.

What symptoms do the fetuses have?

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
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