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
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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