Twin-Twin Transfusion Syndrome - TTTS
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Twin-Twin Transfusion Syndrome - TTTS
من طرف Just a doctor الأحد سبتمبر 12, 2010 1:03 am
Overview
Most pregnancies result in one baby.
In about one in 80 pregnancies, twins
are conceived. This can occur in one
of two ways
The more common way
(which accounts for two-thirds of
cases) is for the two different sperm to
fertilize two different eggs,
resulting in what is called a
dizygotic (DZ) twin gestation. These
twins are often called fraternal twins.
In this type of twinning each twin has its own
sac of amniotic fluid and its own placenta
(afterbirth). Dizygotic twins have two sets of
membranes surrounding their amniotic fluid
sacs (one inner amnion layer and one
outer chorion layer), and therefore
they are known as diamniotic, dichorionic.
In
about one-third of twin pregnancies, one
sperm fertilizes one egg, but this splits into
two embryos resulting in what is known as
monozygotic (MZ) twins. These twins are often
referred to as identical twins since they
have the same genetic material.
Approximately one-third of MZ twins
look just like fraternal twins on
prenatal ultrasound since there are two
separate amniotic sacs and two separate
placentas. However, in two-thirds of identical
twins, each twin has its own amniotic sac but
shares a common placenta. This type
of MZ twinning is called monochorionic,
diamniotic since there is an inner layer
surrounding the amniotic sac of each
twin, but there is only one common
outer layer (chorion) surrounding
both of the sacs. This type of
twinning occurs in approximately one in 360
pregnancies. Monochorionic twins are at higher
risk for complications since they share a
common placenta.
Less
than 1 percent of identical twins (about
one in 2,400 pregnancies) will have one
amniotic sac and one placenta for both twins.
This type of twinning is referred to as monchorionic,
monoamniotic twinning. These twins
are at very high risk for loss of the
pregnancy due to entangled umbilical
cords.
What is Twin-Twin Transfusion Syndrome and how does one get it?
This
condition occurs only in those
identical twins that are
monochorionic, diamniotic (one-third of all
identical or monozygotic twins). In almost all
of these pregnancies, the single
placenta contains blood vessel connections
between the twins. For reasons that are not
clear, in 15 percent to 20 percent of
monochorionic, diamniotic twins, the
blood flow through these blood vessel
connections becomes unbalanced,
resulting in a condition known as twin-twin
transfusion syndrome (TTTS). This is not an
inherited or genetic condition. It is not
caused by something that a mother or father
has done or not done.
In TTTS, the smaller twin (often
called the donor twin) does not get
enough blood while the larger twin
(often called the recipient twin)
becomes overloaded with too much blood.
In an attempt to reduce its blood
volume, the recipient twin will
increase the urine it makes. This
will eventually result in the twin
having a very large bladder on ultrasound, as
well as too much amniotic fluid around this
twin. This is known as polyhydramnios.
At
the same time, the donor twin will
produce less than the usual amount of
urine. The amniotic fluid around the
donor twin will become very low or
absent. This is known as oligohydramnios.
As
the disease progresses, the donor
will produce so little urine that its
bladder may not be seen on ultrasound. The
twin will become wrapped by its amniotic
membrane (known as a “stuck” twin). Often the polyhydramnios
of the recipient twin is the first
thing noticed by the patient due a
sudden increase in the size of the uterus.
Clothes may become tight fitting over a short
period of time. At other times the differences
in the amniotic fluid volumes between the
twins is only noted at the time of a
routine ultrasound.
Illustration: Anastomosis
How is Twin-Twin Transfusion Syndrome diagnosed?
The diagnosis of TTTS is made with an
ultrasound evaluation that shows a
twin pregnancy with one placenta,
twins of the same sex in separate
amniotic sacs, and polyhydramnios in
the recipient’s sac and oligohydramnios in the
donor’s sac. Amniotic fluid volume is measured
with ultrasound by determining the deepest
pocket measurement from the patient’s skin to
her back. This measurement is known
as the maximum vertical pocket (MVP).
What
are the Twin-Twin Transfusion
Syndrome five stages of
classification?
Quintero1
has proposed five stages of TTTS based on
ultrasound findings:
Stage I: This is the
initial way that TTTS is seen on
ultrasound. In stage I, there is
oligohydramnios in the donor’s sac with an MVP
of two centimeters or less (three-quarters of
an inch) and polyhydramnios in the recipient’s
sac with a maximum vertical pocket of fluid
of eight centimeters or more (just
over three inches). The bladder of
the donor baby is still seen.
Stage II: As defined above,
there is polyhydramnios and
oligohydramnios, but the bladder is
no longer seen in the donor twin
during the ultrasound evaluation.
Stage III: Blood flow in
the fetus can be measured with a
special type of ultrasound called
Doppler. In addition to the findings of
Stages I and II, careful study of the blood
flow in the umbilical cord and fetal ductus
venosus (the large blood vessel in the fetus
that returns blood to the heart from the
placenta) reveals abnormal patterns in
Stage III. These patterns can occur
in either or both fetuses.
In the umbilical cord, the diastolic
flow can be either absent or reversed
in the umbilical artery. This
pattern is usually seen in the donor
twin. In the ductus venosus, the
diastolic flow can either be absent or
reversed. This pattern is usually see in the
recipient twin due to early heart failure. The
recipient twin can also exhibit leakage across
the main valve on the right side of the
heart – this is known as tricuspid
regurgitation.
Stage IV: One or both
babies shows signs of hydrops. This
means there is excess fluid in parts
of the baby such as swelling of the
skin around the head (scalp edema), fluid in
the abdomen (ascites), fluid around the lungs
(pleural effusions) or fluid around the heart
(pericardial effusion). These findings are
evidence of heart failure and are
typically seen in the recipient twin.
Stage V: One or both
babies have died. The survival of the
twins is poorer when there is
progression to a higher stage over time. It
has been estimated that half of patients will
progress to a higher stage, 30 percent will
remain at the same stage and 20 percent will
improve to a lower stage.2, 3
What
is an acardiac twin or twin reversed
arterial perfusion (TRAP) syndrome?
An usual form of TTTS occurs in about
one in 15,000 pregnancies. In these
monochorionic twins, one twin
develops normally while the other
twin fails to develop a heart as well as
other body structures. The abnormal twin is
called an acardiac twin. In these
pregnancies, the umbilical cord from the
acardiac twin branches directly from the
umbilical cord of the normal twin. Blood flow
to the acardiac twin comes from the normal
twin, which is also known as a pump twin.
This blood flow is reversed from the
normal direction leading to the name
for this condition: twin reversed
arterial perfusion syndrome or TRAP.
In some cases the blood flow from the
pump twin to the acardiac twin stops
on its own and the acardiac twin stops
growing. In other cases, the flow continues
and the acardiac twin continues to increase in
size. This eventually leads to heart failure
and polyhydramnios in the pump twin. Without
treatment, more than 50 percent of
cases of TRAP will result in the
death of the pump twin.
What is the outcome for Twin-Twin Transfusion Syndrome (TTTS)?
There are a number of ways to treat
TTTS, any of which many be the
correct method depending on
ultrasound findings, the gestational age of
the pregnancy and a couple’s specific needs.
Left untreated, TTTS prior to 24
weeks’ gestation (six months of
pregnancy), 80 percent to 90
percent of cases are associated with the loss
of one or both twins. If one of the
twins should die, the blood vessel
connections in the placenta can place
the surviving twin at risk for
long-term brain damage in as many as
one-third of cases. In general, more advanced
stages of TTTS have a worse prognosis than the
earlier stages. When severe TTTS occurs at a
very early gestational age (prior to sixteen
weeks or the fourth month of
pregnancy), the option of termination
of the pregnancy can be considered
due to the grim prognosis.
The various therapies that are
available target either the unequal
fluid between the twins’ sacs or
interrupt the blood vessel
communications between the twins on the single
placenta. The successful outcome of these
treatments has been based on the number of
babies that survive, as well as the number of
babies who do not have brain damage. The
treatments that are currently
available are described below:
Treatments
Reduction amniocentesis
Serial amniocentesis involves the
removal of the excessive amniotic
fluid from the sac of the recipient
twin using a needle that is passed
through the maternal abdomen.
The amount of amniotic fluid removed
will vary based on the initial volume
in the recipient sac, the
gestational age and the development
of uterine contractions during the
procedure. As a general rule no more than
three liters (approximately two and one-half
quarts) of amniotic fluid is removed at any
one time. The procedure is usually completed
within 30 minutes or less. The procedure may
temporarily restore the balance in
the amniotic fluid in both twins’
sacs. This technique may be useful
for milder cases of TTTS that occur later in pregnancy.
However, reduction amniocentesis
usually requires repeat procedures to
be undertaken every few days to
weekly when the fluid returns to high
levels. The procedure is generally
not thought to be effective for more
advanced stages of TTTS (Stages III and IV).
Complications of repeated
amniocenteses for the treatment of
TTTS include premature labor with
early delivery in 3 percent of cases,
premature rupture of the membranes in 6
percent of cases, infection in about 1 percent
of cases, and premature separation of the
placenta from the wall of the womb (called an
abruption) in 1 percent of cases.4
Pregnancies managed with serial
reduction amniocentesis on average deliver
by 29 to 30 weeks of gestation
(approximately ten weeks prior to the
“due date”).4, 5 If there is
progression of TTTS to a more
advanced stage, serial amniocenteses will
reduce the success rate for such procedures
such as laser (see below). Reported survival
rates have varied from 18 to 83 percent,
with a recent study noting that just over half
(56 percent) of severe TTTS cases
managed with reduction amniocentesis
will end with at least one infant
without brain damage.5 Approximately,
20 percent to 25 percent of the TTTS
survivors from pregnancies treated with
reduction amniocentesis have been found to
have long-term developmental delay.
Illustration: Reduction Amniocentesis
Septostomy (also known as microseptostomy)
Septostomy
is the creation of a hole in the membrane
between the babies’ sacs using a needle. This
causes fluid to move from the amniotic sac
with excessive fluid (the recipient’s sac)
into the sac with absent or low fluid
(donor’s sac). Since septostomy is
performed with a needle that is used
to perform amniocentesis,
complications of infection, premature labor
and premature rupture of the membranes are
rare. Septostomy carries the additional
potential risk for the hole to become larger
between the two sacs and could even allow the
babies to share the same amniotic space
if the entire separating membrane
becomes disrupted. This has been
reported to occur in 3 percent of
septostomies.6 In the worst case
scenario, the umbilical cords of the twins
could become entangled, leading to the death of
one or both fetuses. In one large series,
survival to birth was 80 percent for at least
one twin and was 60 percent for both
twins.6 Patients undergoing
septostomy typically require fewer
procedures than those treated with
amnioreduction. There is no data
currently available regarding neurologic
outcome in survivors of septostomy.
Illustration: Septostomy (also known as Microseptostomy)
Selective laser
ablation of the placental anastomotic vessels
In more advanced stages of TTTS (Stage
II and higher) laser ablation of the
communicating vessels on the
placenta between the twin fetuses can
be a curative procedure.
The procedure is performed in an
operating room. After the patient’s
abdomen has been washed with an
antiseptic and covered with sterile
paper drapes, an ultrasound is
performed to determine the appropriate spot to
enter the uterus. The skin is then injected with
an anesthetic medication to “numb” the area
and deep tissues directly under the
selected site. An anesthesiologist
will also administer medications
through an intravenous line to
produce sedation. A small skin cut is made to
allow the introduction of a thin hollow tube
and needle. The instruments are inserted under
ultrasound guidance into the amniotic sac of
the recipient twin. The needle is
removed and a telescope (fetoscope)
with a thin fiber to carry the laser
energy is then inserted through the
hollow tube. The fetoscope is used to
look directly at the blood vessels on the
surface of the placenta. Vessels that are
found to communicate between the twins are
then closed using laser light energy. At the
completion of the surgery, the extra amniotic
fluid in the recipient twin’s sac is
removed to achieve a normal volume.
The procedure may take 45 minutes to
two hours depending on the difficulty
of the case.
Because the fetoscope requires a
larger hole to be made into the
amniotic cavity than would be the
case with an amnioreduction or
septostomy procedure, laser ablation is
associated with a higher risk of complications
such as premature contractions, premature
rupture of the membranes (15 percent to 20 percent of
cases), placental separation (2
percent) and infection. For this
reason, special medications to
prevent contractions and antibiotics
to prevent infection will be given
before and after the procedure. In addition,
laser therapy may be associated with unique
risks since the laser energy may cause certain
areas of the placenta or blood vessels on the
surface of the placenta to bleed.
Laser ablation has been shown to
result in the survival of at least
one twin in 70 percent to 80 percent
of cases and both twins in one-third of
cases.5, 7, 8 Should one fetus die
after the procedure, the likelihood that the
surviving fetus will develop complications is
reduced from 35 percent to approximately 7
percent. This is because the babies are no
longer sharing blood vessels between
them. In one-third of cases, neither
twin will survive. Studies to date
have indicated that approximately 8
percent of survivors following laser
ablation will have a long-term mental
handicap. This is approximately half of the
rate of problems seen in survivors treated
with amnioreduction.5
Illustration:
Laser Ablation of the placental anastomotic
vessels
Selective cord coagulation
In some cases, a couple may make the
difficult decision to proceed with
the purposeful loss of one twin to
save the other twin. This procedure
is used when laser ablation of the
connecting vessels is not possible or if one
of the twins is so close to death that laser
ablation would likely not be successful. By
stopping the flow in the cord of the dying
twin, the other twin can be protected from
the consequences of its sibling’s
death. The procedure is performed
through the use of a special forceps
that is placed into the amniotic sac
of the recipient twin while watching
with ultrasound. The umbilical cord
is then grasped and electrical current is
applied to burn (coagulate) the blood vessels
in the cord so that the blood flow will stop
to this fetus. The communication between the
fetuses is definitively ended; however,
this eliminates the chance of
survival for one of the twins.
Complications of this procedure
include premature delivery and premature
rupture of the membranes. Rupture of the
membranes has been reported to occur in about
20 percent of cases. Survival of the one
remaining fetus can be expected in 85 percent
of cases.
Illustration: Selective cord coagulation
Radiofrequency ablation
This procedure is usually reserved for
TRAP sequence. The umbilical cord of
the acardiac fetus is usually very
short and difficult to see on
ultrasound. As a result, it is often
difficult to stop the blood flow into the acardiac fetus by coagulation
of the umbilical cord. For this
reason, a major blood vessel in the
acardiac fetus is often targeted as the
site for occlusion of blood flow. This can be
accomplished through the use of a
radio-frequency ablation catheter. In this
procedure, a specialized needle is passed into
the amniotic fluid and then into the body of
the acardiac fetus. A special current
is then applied to the needle to burn
the area around the major blood
vessel in the abnormal fetus. This
will stop the blood flow and allow the
pump twin (normal twin) to no longer have to
send blood to the acardiac twin. Complications
of infection, premature contractions and
premature rupture of the membranes can occur
as in any needle procedure. In one
series, the risk for premature
rupture of the membranes was 8
percent.9 In this same series, the
chance for a successful live birth
for the pump twin was 90 percent.
Illustration: Radiofrequency Ablation
What
do I do after my physician has made a
referral for me to be seen?
You
will be scheduled for an ultrasound evaluation
with one of our maternal-fetal medicine
specialists at Baylor College of Medicine's
Baylor Clinic. The physician will discuss all
findings and will review the treatment
options, surgical procedures, prognosis, and
recommended follow-up care. We will be able to
answer your questions and concerns at
this time.
Next, you will meet with or have a phone
conversation with our fetal therapy
coordinator who will be able to answer any further
questions that you and your partner may have. In addition, the
fetal therapy coordinator will assist you with any special
needs, including overnight
accommodations. You will receive a
folder that contains information you
will need for surgery and additional
information that you will find
helpful.
After your ultrasound and consultation, you will have a
pre-operative consultation with an anesthesiologist, which
will be held in the labor and delivery unit of
St. Luke's Episcopal Hospital. You
will also have blood samples drawn at that
time. A surgery consent form will be given to
you to review. It explains the surgery in
terms you can understand. You will also be
given several consent forms for collection
of data for an ongoing study of
research to help us better understand
the treatment of twin-twin
transfusion syndrome. You will then
be discharged home or back to your hotel room.
How do I prepare for surgery?
The night before surgery, you will not
be allowed to eat or drink for a
defined amount of time (usually six
to eight hours). This is to prevent
the risk of vomiting during surgery.
In medical terms, this is known as "NPO"
(nothing by mouth). We will give you a time to
come to St. Luke's Episcopal Hospital on the day of
surgery.
Your family may come with you, but will be
asked to wait for you in one of our labor or waiting
rooms during the surgery. An intravenous line
(IV) will be inserted by needle stick to give
you fluids and medications during surgery. An
ultrasound will be performed prior to going
to the operating room to confirm that
both twins are alive. One of the
specially trained nurses that will be
assisting in surgery and an
anesthesiology resident will accompany you to
surgery.
What can I expect during surgery?
You will be transported to the
operating room where you will be
asked to move on to the operating
table. You will be covered with a
warm blanket and a pillow will be placed under
your knees to keep you comfortable during
surgery. You may be rolled to your left side
to keep your uterus from causing your blood
pressure to fall. A belt will be placed
across your legs to prevent you from
sliding off the operating room table.
Your abdomen (belly) will be cleaned
with an iodine solution (let your
nurse know if you are allergic to
iodine). Then you will be covered with sterile
paper drapes. The top of the drapes will be
attached to a pole so that you do not need to
watch the procedure. Medication will be given
through your IV to relax you. Surgery
is performed under local anesthesia,
meaning you are awake but relaxed,
and your abdomen is numbed where the
instrument is inserted. An
anesthesiologist will stay with you throughout
the procedure. You will be given additional
medication for discomfort as needed. On rare
occasions, general anesthesia, meaning you are
put to sleep, may be used. During
surgery, one or two small incisions
approximately one-tenth of an inch
long will be made on the abdomen.
These incision(s) are small. You will
have short pieces of specialized tape (steri-strips)
placed on your skin to close this incision at
the end of the procedure.
What can I expect after surgery?
Following surgery, you will be taken
to the recovery room in labor and
delivery or a labor room where you
and your fetus or fetuses will be
closely monitored. Your abdomen will be
a little tender or sore once the local
anesthetic wears off. You may be given
medications after surgery to relax the uterus
and stop any contractions. The pain and
discomfort after surgery is usually minimal.
If needed, pain relief medicine is available.
Your spouse or other support person
may remain with you in your room.
Following surgery, you may have food
as tolerated. You will be admitted to
the hospital for an overnight stay.
That night, activity is restricted to
bathroom privileges only, but this
depends upon your specific condition. You
will undergo an ultrasound the day after
surgery to determine how the babies are doing.
What can I expect after I am discharged home?
You will then be discharged home to
the care of your primary obstetrician
and/or your referring maternal-fetal
medicine specialist. Your
instructions will include bed rest with
bathroom privileges for seven days after the
surgery, with a gradual increase in activity.
We will also ask that you get a thermometer
and take your temperature three times per
day. You should notify your primary
obstetrician for any increase above
100.4°F of an oral temperature. The
site of the surgery can get wet in a
shower within 24 hours of the
procedure. You can remove the steri-strips over
the incision yourself one week after the
surgery.
After four weeks you can resume
normal activity based on your pregnancy
condition and the comfort level of your
primary obstetrician. Weekly ultrasounds are
recommended for the next month. After that
time, if all is going well, ultrasounds are
performed as directed by your doctor.
Although you are returning home, we
will continue to follow your
pregnancy closely through our care
coordinator. Please make arrangements with
your doctor to forward your ultrasound reports
and any other pertinent information to us. We
also ask that you inform your obstetrician and
labor nurse that we would like to
have your placenta sent back to us
after you delivery. This information
is useful to further our knowledge
and will assist in the future
treatment of patients with TTTS.
Social services and pastoral care are
available for all our patients and
their families. If you would like to
see them at any time, you need only
to request it and they can be
contacted. We are sensitive to the
psychological, social and spiritual needs of
our families. We will provide any support that
is necessary. Please contact us if you have
any questions, concerns or special requests.
For our out of town patients, we
realize that traveling may be
difficult or stressful and want you
to know that we will do everything we
can to accommodate your special needs and
schedule
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- عدد المشاركات : 4835
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تاريخ التسجيل : 20/07/2010
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