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What is twin-to-twin transfusion syndrome?

TTTS is condition if identical twin  pregnancies where both babies share the same placenta. Connections between the babies within the placenta are common, and usually balance each other out. On occasions the connections are unbalanced and one baby ends up losing blood chronically into his or her sibling. The baby losing blood is called the donor, and the one receiving the blood is called the recipient.

Over time the donor becomes dehydrated and fails to grow properly. The amniotic sac for the donor becomes empty and the membranes wrap closely around the baby. At this point the donor is sometimes called the "stuck" twin, because he or she cannot move freely.

The recipient, on the other hand, becomes over-hydrated and swollen. His or her amniotic sac becomes over-full of fluid (polyhydramnios) and the uterus may become very distended. The recipient eventually develops heart failure when he or she can no longer cope with the extra blood volume.

How common is it?

Twins occur naturally in 1 in 84 pregnancies. About one third of twins are identical and two thirds of them share the same placenta. 10-20% of these twins end up with some degree of unequal sharing of blood. For 2000 pregnancies, therefore, one may have twin to twin transfusion syndrome.

How is it diagnosed?

TTTS is usually diagnosed early in the pregnancy by ultrasound. The characteristic appearance of low fluid in one sac (oligohydramnios) and excess fluid in the other (polyhydramnios) must always be present. As the condition advances, the bladder of the donor becomes too small to see, and blood flow in the umbilical cord and heart of the babies becomes abnormal. In advanced cases the recipient appears swollen (hydrops) and one or both of the babies may be dead.

What is the outcome?

Without treatment the babies die in 80-90% of cases. The outcome is dramatically improved with treatment.

Are there any treatments available?

There are a number of proposed treatments for TTTS.

Because the outcome has the potential to be so poor, many families opt to terminate their pregnancy if a severe early case of TTTS is diagnosed. Alternative therapies are available that attempt to either equalize the pressure between the two sacs or interrupt the connection between the babies. These therapies will be described below and are: 

1. Aggressive reduction amniocentesis

2. Septostomy, and

3. Selective laser ablation of the connecting vessels.

Aggressive reduction amniocentesis

Serial amniocentesis is the removal of the excessive fluid from around the recipient twin using a needle. This procedure may temporarily restore the balance in the amniotic fluid volumes of both. This technique may be useful for milder cases of TTTS, and is often recommended in these cases, but is generally not effective for severe cases. Generally, the need for many amniocentesis procedures has been shown to result in a 40-60% survival rate of at least one of the twins, with approximately 25% of the survivors mentally handicapped.


Septostomy is the creation of a hole in the membrane between the babies using a needle.  This causes fluid to move towards the donor’s side and balance the fluid levels.  Septostomy has not been shown to be a successful therapy, especially in stage 2-5 cases and may create complications such as amniotic bands and cord entanglement.

  Umbilical cord ligation

Umbilical cord ligation is an technique that involves tying a knot around the cord of one of the twins to stop its heart from beating, stopping the communication between the fetuses.  This is done using similar instruments to the fetoscope. This procedure is used when one of the twins is so close to death that laser ablation is not possible, and is done to protect the other twin from the consequences of that death. The communication between the fetuses is definitively ended, however, this eliminates the chance of survival for one of the twins.

Selective laser ablation of the connecting vessels

For the more severe stages of TTTS, this is the only curative therapy. Laser photocoagulation is the use of laser light to close the blood vessels on the surface of the placenta so that the babies’ blood is no longer shared.

The placenta is inspected with a very thin telescope called a “fetoscope”. The fetoscope is placed into the uterus through a tiny hole in the skin and under an anesthetic and so is not painful. The telescope identifies the small connecting blood vessels and they are then “coagulated” using laser light from a small fiber passed along it. The surgery is done in an operating room and takes 30-60 minutes. The type of anesthetic is decided between you, the surgeon and the anesthetist, but we recommend an epidural. 

Generally, fetoscopic laser ablation has been shown to result in a 60-70% survival rate of at least one of the twins, with approximately 5% of the survivors mentally handicapped.  

A recent prospective randomized trial (the Eurofetus study) comparing laser ablation to alternative therapies has demonstrated significantly improved survival with a reduction in the rate of mental handicap in the surviving babies.

If you wish to print out an information sheet about Selective Laser Ablation Therapy at the Evergreen Fetal Therapy Center, click here. The same information is also available as a web page here.

The link below will take you to a slide presentation about laser ablation therapy, its outcomes and advantages: Minimally Invasive fetal therapy



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Last modified: April 16, 2009