Twin to Twin Transfusion Syndrome is a disorder in identical twin pregnancies where one twin donates,
or transfuses, much more blood than it receives from the other, through their shared placenta.
This can cause problems for both twins. We don’t completely understand what causes the disease,
but it does not appear to be caused by genetics, environmental factors or habits during pregnancy.
Identical twins happen when a single fertilized egg splits in two
and forms two embryos which have identical DNA. In the majority of cases of identical twins,
each twin has a separate amniotic sac, and shares a single placenta.
The placenta brings oxygen, nutrients and other supplies from the mother, to the babies.
It also removes waste that the babies produce as well.
Normally, the baby’s blood travels from the placenta, to the baby, and back again,
via its umbilical cords.
In identical twins, however, some blood vessels from one twin can connect to the other twin,
sharing blood between the twins. This happens in almost every identical twin pregnancy with a
shared placenta. The number of these connections can vary greatly from person to person,
and most are on the surface of the placenta, though some are deeper.
There are three ways the blood vessels can connect to each other: an artery can connect to an artery,
a vein can connect to a vein, or an artery can connect to a vein.
In about 85% of cases, the blood flow between the twins is balanced.
However, 15% of the time, the blood flow is not balanced,
and one twin, the “Donor,” donates more blood than it receives back from the “Recipient.”
Because the Donor gives away blood, it also makes less urine, resulting in less amniotic fluid and
a smaller amniotic sac. The Recipient, however, makes much more urine than it normally would,
due to the extra fluid it receives from the Donor.
This results in more amniotic fluid and a much larger amniotic sac.
When this happens, the twins have entered stage 1 of Twin to Twin Transfusion Syndrome.
In stage 1, there is a noticeable size difference between the amniotic sacs.
In stage 2, the Donor is giving away so much blood and producing such little urine,
that its bladder is no longer visible in an ultrasound.
By stage 3, the abnormal blood flow is detectable by an ultrasound.
The recipient’s heart may start to show signs of not working as well as expected.
A difference in size between the twins may also be noticeable by this stage, although this may
be seen earlier as well. In stage 4, there are signs of heart failure in one or both twins.
In severe cases, we will recommend laser surgery, or laser “ablation”. This is a
minimally invasive procedure done on the placenta to stop the unequal blood flow between the twins.
Treatment can be started within hours or days of diagnosis. First, we will discuss what type
of anesthesia is best for you. You will be continuously monitored, and neither you or
your twins will feel any pain or discomfort during the procedure. The entire procedure
is done by a single instrument: the fetoscope. It contains a camera, a suction tube, and the laser.
A small incision, smaller than the width of a pencil, is made.
Next, an ultrasound is used to carefully guide the fetoscope into your uterus
and into the Recipient’s sac.
Next, the team studies the placenta, mapping out all the connections between the twins.
Then, each one is systematically sealed off, or “ablated” with the laser.
The number of connections can vary widely between patients.
Only the connections shared between the twins are treated. This greatly reduces
the unequal blood flow between the twins, stopping twin to twin transfusion syndrome.
Finally, the surgeon removes the excess amniotic fluid from the Recipient’s sac.
After the procedure, you will stay with us overnight as you recover from surgery.
In most cases patients can go home the next day. We usually recommend an
ultrasound within a week after surgery before returning to care with your obstetrical team.
Even with the best care, there is a significant risk of early delivery, and other complications,
so we will continue to partner with your providers to ensure the best care for your pregnancy.
At the Colorado Fetal Care Center at Children’s Hospital Colorado,
our multidisciplinary team are experts in Twin to Twin Transfusion Syndrome.
We provide 24/7 care, and have some of the most advanced imaging capabilities in the
country, with one of the few dedicated labor-and-delivery-units in the nation.
To learn more, call us, click the links here, or check the description below.