Twin to Twin Transfusion Syndrome Skip To Content

Twin to Twin Transfusion Syndrome

Twin to Twin Transfusion Syndrome (TTTS) occurs only in identical twins that share one placenta, two amniotic fluid sacs (diamniotic) and are monochorionic (share one chorian – the outer layer of the amniotic sac). Approximately 15 to 20 percent of these type of twins develop TTTS. Blood vessels from the shared placenta connect the twins and, for reasons that are not clear, the blood flow between the twins becomes unbalanced, resulting in one twin not getting enough blood and the other becoming overloaded with too much blood. As a result, the smaller twin (also called the donor twin) does not get enough blood and reacts by not producing enough urine. Fetal urine is what amniotic fluid is made from. This lack of amniotic fluid is called oligohydramnios. The donor's bladder may become very small and unable to be seen on ultrasound. The larger twin (called the recipient) gets too much blood and then produces an excess of urine in an attempt to reduce the blood volume, resulting in too much amniotic fluid. This is called polyhydramnios. The recipient's bladder becomes very large and is apparent on ultrasound.

Twin to Twin Transfusion Syndrome is a progressive disease and is often categorized into five stages. Mothers may first be alerted by a sudden, unusual increase in abdominal size or the condition may not be noticed until a regular ultrasound reading. Left untreated, the disease is often fatal for both twins

How Do You Get Twin to Twin Transfusion Syndrome?

Twin to Twin Syndrome is not known to be caused by genetic or inherited factors. It is not caused by anything the mother or father has or has not done. The exact causes are not known at this time. It can develop at any time during a pregnancy involving identical twins sharing a placenta who are diamniotic and monochorionic.

How is Twin to Twin Transfusion Syndrome Diagnosed & Staged?

Twin to Twin Syndrome is diagnosed by ultrasound. Typically, the ultrasound shows a twin pregnancy with one placenta, same sex twins in separate amniotic sacs, and polyhydramnios in the recipient's sac and oligohydramnios in the donor's sac. The ultrasound sonographer will measure the amniotic fluid volume by determining the deepest pocket measurement from the mother's skin to her back. This measurement is called maximum vertical pocket (MVP). Blood flow in the babies' umbilical cords and fetal ductus venosus (large blood vessel that returns blood to the baby's heart from the placenta) can be measured by special Doppler ultrasound. The following are the five stages your maternal-fetal medicine specialist will use to determine the progression of the disease.

Stage I: There is oligohydramnios in the donor's sac, but the donor baby's bladder is still visible on ultrasound. The MVP in the donor's sac measures three-quarters of an inch or less (less than two centimeters). Polyhydramnios is seen in the recipient's sac, with a fluid MVP of just over three inches (eight centimeters).

Stage II: The same conditions as Stage I exist, except the bladder in the donor twin is no longer visible on ultrasound.

Stage III: Doppler ultrasound may indicate abnormal blood flow patterns in one or both of the twin's umbilical cords and fetal ductus venosus. The conditions seen in Stage I and Stage II continue to exist.

Stage IV: One or both babies show signs of excess fluid in different parts of their bodies (called hydrops). Swelling of the skin around the head, fluid in the abdomen, around the lungs and around the heart may be seen. These findings are typically seen in the recipient twin and are signs that a baby's heart is failing due to being overloaded by more blood than it can process.

Stage V: One or both of the babies have died. The higher progression of the disease often results in a poorer prognosis for the twin's survival or being born without brain damage. Studies have shown that approximately 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.

What is Acardiac Twin or Twin Reversed Arterial Perfusion (TRAP) Syndrome?

This is a rare form of Twin to Twin Transfusion Syndrome where one twin develops normally while the other twin fails to develop a heart as well as other body structures. The abnormal twin (the one missing a heart) is called acardiac. Blood flows from the normal twin's umbilical cord that branches directly into the abnormal twin. This blood allows the acardiac twin to continue to grow in size. The normal twin providing the blood flow is often called the pump twin. Blood flow is reversed from the normal direction leading to the name: Twin Reversed Arterial Perfusion or TRAP. Sometimes the blood flow to the acardiac twin will stop on its own and the abnormal twin will stop growing. If the blood continues to flow to the acardiac twin it will continue to grow in size. However, the added stress on the pump twin will lead to heart failure and polyhydramnios. Left untreated, more than 50 percent of pump twins will die from TRAP. The acardiac twin is unable to live outside of the uterus since it does not have a heart or the body structures needed to survive.

What Does Twin to Twin Transfusion Syndrome Mean for My Baby?

Left untreated, 80 to 90 percent of twins diagnosed with TTTS prior to six month's gestation (24 weeks) will result in the death of one or both twins. If one twin dies while in the uterus, it places the surviving twin at risk for long-term brain damage in one-third of cases. The more advanced stages of TTTS have worse prognosis than earlier stages. If severe TTTS occurs very early in pregnancy (prior to the fourth month or 16 weeks) some patients consider terminating the pregnancy due to the poor prognosis of survival and incidence of brain damage.

Twin to Twin Transfusion Syndrome survivors may have developmental delays, brain damage and other complications caused by the disease or by premature delivery.

There are a variety of treatments for TTTS and the best course for your babies will vary depending on their condition, their stage of TTTS, any other risk factors involved and your maternal-fetal medicine specialist's recommendations.

If I am Diagnosed with Twin to Twin Transfusion Syndrome, What Happens Next?

If your primary care doctor suspects TTTS, you will be referred to a maternal-fetal care center for further evaluation and confirmation of the diagnosis. Your maternal-fetal medicine specialist will have you undergo another detailed ultrasound and other diagnostic tests that will help confirm the diagnosis and stage the progression of the disease. You will have all the information about what is happening with your twins explained in terms that are easy to understand, and your specialist will explain treatment options, the risks and benefits of each and will make a recommendation for a care plan to manage your pregnancy. You may be treated at Sanford Maternal-Fetal Care Center, or if needed, you may be referred to another national fetal care center to receive necessary treatment.

How is Twin to Twin Transfusion Syndrome treated?

There are a variety of treatments for TTTS. Your maternal-fetal medicine specialist will provide you with the best recommendation of treatment for your pregnancy, and will review all the risks, pros/cons and expected outcomes of the treatment options. Treatments often focus on the unequal fluid between the twins or on interrupting the blood vessel connections between the twins. The following are overviews of common treatments. Please talk with your maternal-fetal medicine specialist to learn more about these procedures and how they may apply to your pregnancy.

Reduction Amniocentesis

This procedure involves repeated removal of excess amniotic fluid in the recipient twin's amniotic sac by using a needle that is passed through the mother's abdomen. The goal is to temporarily restore fluid balance in the amniotic sacs of both twins. This technique if often useful for milder forms or stages of TTTS that occur later in pregnancy. Since the fluid return to high levels after some time, this often needs to be repeated every few days or weekly. Risks include premature labor, premature rupture of membranes, infection, premature separation of the placenta from the wall of the uterus and if the TTTS progresses to a more advanced stage, this procedure may reduce the success rate of other treatments.

Pregnancies managed by this technique have the following statistics:

  • Average delivery at 29 to 30 weeks gestation – about 10 weeks before the due date
  • Survival rates vary from 18 to 83 percent
  • Just over 50 percent of severe TTTS cases end with at least one baby without brain damage
  • Nearly 20 to 25 percent of TTTS survivors managed by reduction amniocentesis have long-term developmental delay

Septostomy (Microseptostomy)

Septostomy focuses on trying to balance the levels of amniotic fluid between the twins by creating a hole in the membrane between the babies' sacs using an amniocentesis needle. The hole allows excess fluid from the recipient twin to flow to the baby without enough fluid. This procedure may also need to be repeated, though usually less often than with reduction amniocentesis. Risks are the same as for reduction amniocentesis, but also include the chance that the hole will become too large and allow the babies to share the same amniotic space – where their umbilical cords could become entangled, leading to the death of one or both.

Pregnancies managed by this technique have the following statistics:

  • Survival to birth 80 percent for one twin; 60 percent for both
  • In three percent the hole becomes too large and disrupts the membrane leading to shared amniotic space
  • No neurological data is available for survivors at this time

Selective Laser Ablation

For more advanced stage of TTTS, laser ablation (destruction) of the blood vessels between the twins on the placenta may cure the disease. This procedure is performed in an operating room at a hospital and the mother will be given anesthetics and sedation. It often requires 45 minutes to two hours. Under the guidance of ultrasound, a small fetoscope (telescope) with a thin fiber that carries the laser energy is inserted through a tiny cut in the mother's abdomen into the sac of the recipient twin. The fetoscope allows the physician to examine the blood vessels on the placenta and to determine which ones are communicating blood flow between the twins. Laser light energy is then used to destroy those specific blood vessels. Once completed, extra amniotic fluid is removed from the recipient twin's sac to restore normal volume.

Risks are higher for this procedure and include: premature contractions, premature rupture of membranes, placental separation and infection. Patients often receive medication to prevent contractions and antibiotics to prevent infection before and after the procedure. Laser therapy also has the risk of causing non-targeted areas of the placenta to bleed.

Pregnancies managed by this technique have the following statistics:

  • Survival of at least one twin in 70 to 80 percent, both twins in one-third cases
  • A reduction from 35 percent to 7 percent of the other twin developing complications should one twin pass away while in the uterus
  • In one third of cases neither baby will survive
  • Approximately eight percent of survivors will have a long-term mental handicap

Selective Cord Coagulation

If laser ablation is not possible or if it is determined that one twin is unable to survive, the difficult decision may be made to save one twin by losing the other. By stopping the flow of blood in the cord of the dying twin, the other twin can be protected from complications that would result if the sibling died suddenly while in the uterus. This procedure is performed using a special tiny forceps inserted through the mother's abdomen. The dying twin's umbilical cord is grasped and an electrical current is used to burn (coagulate) the blood vessels in the cord so that blood flow to the twin stops. The surviving twin will no longer have irregular blood flowing from the donor twin. Risks involved in this procedure include premature delivery and premature rupture of membranes.

Pregnancies managed by this technique have the following statistics:

  • Survival of the one remaining twin is 85 percent
  • A 20 percent chance of premature rupture of membranes

Radiofrequency Ablation

This procedure is primarily used for TRAP cases. Because the umbilical cord in the acardiac fetus is very short and hard to see on ultrasound, stopping the blood flow with coagulation of the umbilical cord may not be an option. Instead, a major blood vessel in the acardiac fetus may be used. A catheter is inserted though the amniotic fluid and into the blood vessel in the acardiac fetus. Radio-frequency and a special current are used to burn the area around the major blood vessel. This will stop the flow of blood to the acardiac twin. The normal twin (pump twin) will no longer have to send blood to the acardiac twin. Risks include infection, premature rupture of membranes, and premature contractions.

Pregnancies managed by this technique have the following statistics:

  • A 90 percent survival rate for the pump twin
  • An 8 percent chance of premature rupture of membranes