Understanding Twin-Twin Transfusion System
• What is twin-twin transfusion syndrome?
• How common is TTTS and what causes it?
• How is TTTS detected during pregnancy?
• How will my pregnancy be managed now that TTTS has
• How will TTTS be treated after birth?
• What is the long-term outlook for babies with TTTS?
• WWhat are the chances I could have another pregnancy
• What can I expect from the specialists at Morgan Stanley Children's Hospital?
WHAT IS TWIN-TWIN TRANSFUSION SYNDROME?
Twin-twin transfusion syndrome (TTTS) occurs in monochorionic
twin pregnancies. Monochorionic twins are identical
twins that usually share a single placenta. In most of these
placentas, there are blood vessels that connect the twins to
each other in a balanced way. In TTTS, there is an unequal
sharing of blood through these connecting vessels resulting
in changes in regional blood flows and/or alterations in
cardiac function in either or both twins. TTTS cannot occur
in fraternal twins which have two placentas. Knowing the
chorionicity or number of placentas in the pregnancy is very
important in determining whether you should be monitored
closely for TTTS. This should be determined by ultrasound
as early as possible in the pregnancy.
In TTTS, there is a donor twin, which donates blood to
the recipient twin. The donor twin tends to have little or
no fluid around it, a small or invisible bladder, and is often
smaller than its cotwin. The recipient twin has too much
fluid around it, an enlarged bladder, and is usually larger
in size. The recipients are often found to have cardiovascular
changes in the later stages of TTTS. At birth, the
donor twin is usually pale and anemic while the recipient
twin is polycythemic (an increase in cell mass of the blood)
and hypervolemic (an increase of fluid in the blood).
HOW COMMON IS TTTS AND WHAT CAUSES IT?
TTTS complicates 10-15% of monochorionic-diamniotic twin gestations.
TTTS cannot be prevented. It appears to be the result of communications
within the single placenta that result in unbalanced blood flow between
the twins. However, there may be other reasons why some identical
twins develop this condition and others do not. There are numerous
studies underway investigating TTTS and interventions that may decrease
the risk of progression of this condition.
HOW IS TTTS DETECTED DURING PREGNANCY?
Once a twin or multiple pregnancy has been diagnosed, it is essential to
know the chorionicity or the number of placentas and amniotic sacs. If twins are found to have one placenta, which is monochorionic, then you
are at risk for developing TTTS. There are specific sonographic criteria
for TTTS using the Quintero staging system:
Depending on the stage of TTTS, you may be offered different
management options which range from observation to in utero placental
- Stage I: Low fluid in donor twin sac (<2 cm) and increased fluid in
recipient twin sac (>8 cm)
- Stage II: Bladder in donor twin not visible, normal blood flow studies
- Stage III: Abnormal blood flow studies in the umbilical artery, umbilical
vein, or ductus venosus
- tage IV: Hydrops (excess fluid in the body cavities) of one or both
- Stage V: Demise of one or both twins
HOW WILL MY PREGNANCY BE MANAGED NOW THAT TTTS HAS
Any pregnancy diagnosed with TTTS needs to be monitored closely
for changes and progression of the disease. The current guidelines
at NewYork-Presbyterian Morgan Stanley Children's Hospital/Columbia
University Medical Center are for weekly ultrasounds to assess the
twins. Fetal echocardiography to evaluate heart function and anatomy is recommended when TTTS is initially diagnosed. Follow-up echocardiograms
will be needed to assess the cardiovascular status in the twins
as the pregnancy advances. When TTTS is detected, consultation with
a maternal fetal medicine specialist experienced in TTTS is offered.
Management options and recommendations will be discussed thoroughly
and may include any of the following:
For every option offered, a thorough explanation of potential risks and
benefits will be discussed as well as support for all decisions made.
These recommendations are individualized based on the condition of the
twins and your specific situation. The Maternal-Fetal medicine specialists
are here to guide you in making whatever decision is right for you and
your family. If you opt for the laser procedure, a MRI to assess the fetal
brains is also recommended 3-4 weeks post-procedure.
- Expectant management
- Amnioreduction (remove the excess fluid around the larger twin
which may promote comfort for the mother and decrease the risk
of preterm labor)
- Laser photocoagulation of communicating blood vessels in the
placenta (performed between 16-26 weeks gestation)
- Selective reduction of one twin to a singleton pregnancy
- Termination of entire pregnancy
HOW WILL TTTS BE TREATED AFTER BIRTH?
The effects of TTTS tend to improve after birth because the twins
are no longer sharing a single placenta. Once the babies are born,
they will need to be assessed by experienced neonatologists and
pediatric specialists familiar with TTTS. There can be health concerns
for the twins including low birth weight, complications of prematurity, and
cardiac abnormalities, particularly in the recipient twin. The specialists
at Morgan Stanley Children's Hospital are well prepared to care for
twins affected by TTTS.
WHAT IS THE LONG-TERM OUTLOOK FOR BABIES WITH TTTS?
Without intervention, the long-term outlook for twins with advanced
stages of TTTS is poor with a perinatal mortality rate of 90%.
Furthermore, of those who survive, there is a 15-50% risk of neurologic
handicap. Treatment can improve survival of one or both twins
to over 50% depending on the stage of the condition and has been
associated with lower neurologic handicap. Survival and long-term
outcomes are related to the severity of TTTS and the response to
WHAT ARE THE CHANCES I COULD HAVE ANOTHER PREGNANCY
While some families may have another multiple gestation, the likelihood
of another identical twin pregnancy affected by TTTS is low. Overall, the
recurrence risk remains the same as it was in the initial pregnancy and
should not be a reason to avoid future pregnancies if desired.
WHAT CAN I EXPECT FROM THE SPECIALISTS AT MORGAN STANLEY CHILDREN'S HOSPITAL?
Morgan Stanley Children's Hospital is well-equipped to handle your
pregnancy and the twin's care after birth. Morgan Stanley Children's
Hospital has consistently been ranked one of the best pediatric
hospitals in the country: our Maternal-Fetal Medicine specialists have
extensive experience with TTTS as well as other complications of multiple
pregnancies. Our NICU is one of the most advanced in the United States,
and has been cited for its excellence and dedication to patient care.
The well-being of you and your twins are extremely important to
everyone involved in your care. Together we are all dedicated to giving
you the best pregnancy and healthiest outlook for your twins.