Twin-twin transfusion syndrome

What is Twin-twin transfusion syndrome (TTTS)?

TTTS is a complication of identical twins, where the twins share a single placenta.  One in every five sets of twins would share a single placenta.  TTTS develops in one in every five sets of twins with a single placenta.  TTTS develops if blood vessels from one twin’s portion of the placenta “short-circuits” to the other twin’s portion of the placenta.   One twin (the “donor”) then little by little pumps some of its blood through the placenta to the other twin (the “recipient”).

If this carries on long enough, the donor twin ends up with less and less blood in its circulation.  It does not grow as well as it should.  It also produces less amniotic fluid.  Eventually, it is “stuck” to the side of the uterus, because there is almost no amniotic fluid in its sac.  It might even die in the uterus, because it does not receive enough nutrients or oxygen to stay alive.  The recipient, on the other hand, grows more quickly. It produces lots of amniotic fluid.  There might be so much amniotic fluid that the mother can notice a sudden increase in size of the uterus, as well as discomfort or pain in the abdomen.  The amount of amniotic fluid might be so much that it causes a miscarriage.  The recipient twin might also develop heart failure, because of the overload of blood in its circulation.

Am I at risk of developing TTTS?

You are at risk if you:

  • Have identical twins that share a single placenta

You are at greater risk if:

  • Your twins differ markedly in size (usually more than two weeks) before 26 weeks of gestational age
  • If the nuchal translucency thickness (measured at 11-13 weeks) of your twins differ markedly
  • You have an increased amniotic fluid volume (called “polyhydramnios”) of one twin.  This might be noted on an ultrasound scan.  You might also become aware of pain or discomfort over your uterus, and that your uterus increases in size rapidly.

When will TTTS be suspected?

  • If you have one of the “at risk” symptoms
  • Sometimes it is difficult to see the membrane between the two amniotic sacs, and the apperance on ultrasound is that of twins sharing a single amniotic sac ( “monoamniotic” twins)

How will TTTS be confirmed?

A careful ultrasound scan with good equipment is needed.  The membrane between the two twins can be very difficult to find, but can be seen close to the donor, “stuck”, twin.  This twin will be small for gestation.  Its mobility is restricted by a lack of amniotic fluid.  It does not move away from the place where it is “stuck” to the side of the uterus.  Its bladder is empty and therefore difficult to see on scan.  The other twin is freely mobile in a large amount of amniotic fluid.  It is larger than the other twin.  Its bladder is prominently filled.  Sometimes there might be signs of fluid collections in its abdominal cavity of thorax if it is developing heart failure (so-called “hydrops”).

 What can be done for TTTS?

  • At first, treatment with medication to reduce the amount of amniotic fluid, suppress contractions, or treat fetal heart failure has been tried.  It does not help.  With or without these medications, less than 5% of twins with severe TTTS would survive.
  • Another option is amniodrainage, where large volumes of amniotic fluid is drained from the amniotic sac of the larger twin.  This could help prolong the pregnancy.  On the other hand, amniodrainage does not alter the underlying problem.  If one twin were to die, the survivor is at high risk of permanent neurological damage because it suddenly loses a large volume of blood into the circulation of the dead twin.
  • The umbilical cord of one twin might be tied of by means of small instruments introduced into the uterus.  This would mean that one twin would die, but gives the other twin a better chance of surviving and developing normally.  Obviously, such a radical step would only be considered after careful consideration of the various options with you.
  • The most accepted option is laser therapy of the blood vessels which cause the “short-circuit” between the two twins’ circulations.  This is also done by small instruments introduced into the womb.  Previously, laser therapy has only been available overseas (e.g. in Europe, England and America), but it has now been performed in South Africa as well.  Overseas, at least one twin survives in 70% of pregnancies with TTTS treated with laser.

Where can I find more information about TTTS?

Some useful internet addresses are:

The UK TTTS association

The USA TTTS foundation