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 been detected?
• 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 with TTTS?
• What can I expect from the specialists at Morgan Stanley Children's Hospital?

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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:

• 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 S

• tage IV: Hydrops (excess fluid in the body cavities) of one or both twins

• Stage V: Demise of one or both twins

HOW WILL MY PREGNANCY BE MANAGED NOW THAT TTTS HAS BEEN DETECTED?
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:

• 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

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 interventions undertaken.

WHAT ARE THE CHANCES I COULD HAVE ANOTHER PREGNANCY WITH TTTS?
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.