Twin-to-Twin Transfusion Syndrome (TTTS)

What Is Twin-to-Twin Transfusion Syndrome?

Twin-twin transfusion syndrome (TTTS) is a condition that occurs in 10-15% of identical twin pregnancies in which the fetuses share a placenta but are in two separate amniotic sacs (monochorionic-diamniotic or “mono-di”). The placenta normally maintains complex blood flow networks that balance the flow going through the umbilical cord of each fetus. However, in TTTS, these networks have abnormal connections to each other that disrupt the normal balance resulting in low blood flow to one twin (donor) and high blood flow to the other twin (recipient).  As a result, the donor twin has low blood pressure, grows poorly, and has low levels of amniotic fluid (oligohydramnios). Conversely, the recipient twin grows well but the increased blood flow leads to high blood pressure that causes heart strain and high levels of amniotic fluid (polyhydramnios). If left untreated, TTTS can lead to extreme prematurity and cause significant injury to the heart, brain, kidneys and other organs in either twin. In the worst cases, it can be fatal for one or both twins.  

How Is Twin-to-Twin Transfusion Syndrome Diagnosed?

It is recommended that all mono-di twin pregnancies undergo screening ultrasounds every other week, starting no later than 16 weeks gestation, in order to look for TTTS and other pregnancy complications. As a result, TTTS is typically discovered during these screening ultrasounds by identifying the oligohydramnios-polyhydramnios (oli-poly) appearance of the amniotic sacs around the babies. As the condition progresses, other signs appear.

Twin-to-Twin Transfusion Syndrome Stages

The Quintero staging system is most commonly used to track the progression of the TTTS:  

  • Stage 1: Oligohydramnios-polyhydramnios appearance only. The donor twin has very little fluid in its amniotic sac and the recipient has too much fluid in its amniotic sac. The urinary bladders for both twins are detectable by ultrasound. 
  • Stage 2: Oligohydramnios-polyhydramnios appearance plus the donor twin’s urinary bladder is no longer detectable by ultrasound. 
  • Stage 3: Abnormal blood flow through the umbilical cord or through the twins’ hearts.
  • Stage 4: Fetal heart failure develops otherwise known as “hydrops”. This situation is detected when swelling or fluid accumulates in the abdomen, around the lungs or heart or under the skin of one or both twins. 
  • Stage 5: In utero death of one or both twins.

How Do We Treat Twin-to-Twin Transfusion Syndrome?

The proper treatment of the TTTS depends on the stage of disease. In most cases of TTTS (stages I-IV) that develop before 28 weeks, we recommend laser surgery as this approach directly treats the cause of the disease – the abnormal connections in the placenta. Sometimes, in the earliest stage I cases, a trial of observation with follow-up ultrasounds may be an option if heart strain has not yet developed or the TTTS has developed slowly after 26 weeks. The heart strain is evaluated by a specialized ultrasound of the fetal heart called a fetal echocardiogram, which is often referred to as a “fetal echo”. The fetal echo helps us to determine which of the patients with stage I TTTS are likely to progress to advanced stages of the disease during a possible observation period. In these cases, observation is not recommended. 

At The Chicago Institute for Fetal Health (CIFH), laser surgery for TTTS is called “selective fetoscopic laser photocoagulation (SFLP)”.  The goals of the SFLP procedure are:

  1. To directly visualize the abnormal vascular connections on the surface of the placenta through a small operating telescope.
  2. To coagulate these connections with a laser fiber.
  3. To remove the excess fluid from the recipient twin’s sac thereby relieving the tension on the mother’s abdomen.

In most cases, the SFLP procedure is done in a sterile operating room with the mother awake but lightly sedated with IV medication. Occasionally an epidural analgesia is preferred and rarely a general anesthesia is required. The specialized fetal anesthesiologist will tailor the anesthetic approach to the needs and preference of each mother. After the skin is cleaned and sterilized, a local anesthetic is administered to a single point on the skin of the mother’s abdomen, similar to the anesthetic for a dental procedure. 

Next, a tiny incision is made through which we will pass a needle-like operating sheath into the amniotic sac of the recipient twin. The entire operation is done within the confines of that sac, because it is a large space filled with extra amniotic fluid due to the TTTS. In addition, all of the vascular connections can typically be seen from this space, as well.  

Once it is in place, the hollow sheath permits the internal passage of the operating telescope and the laser fiber so that the operation can be done inside the uterus under the direct vision of the surgeon. Each of the abnormal vascular connections is identified and catalogued providing a “road map” for the surgery. Then, with a high degree of precision, the vascular connections are efficiently coagulated with the laser fiber along this road map, taking great care to avoid injury to the normal vascular networks. 

After the laser portion of the SFLP procedure, the placental circulation is functionally separated so that there is no longer any significant sharing of the placental blood supply between the babies. Finally, the excess fluid is removed from the recipient twin’s amniotic sac bringing the level into the normal range, which helps with the early recovery after the procedure and relieves the tension on the mother’s abdomen. The operating sheath is then removed and the skin incision closed with a single absorbable stitch covered with surgical glue.

What Is the Recovery Like After Surgery for Twin-to-Twin Transfusion Syndrome?

Most mothers spend less than 24 hours in the hospital after the operation. The first few hours include monitoring on the post-operative labor and delivery recovery area before being transferred to the maternity ward if no concerns arise. There, the mothers are typically allowed to eat, drink and move around to use the bathroom, etc. while being monitored intermittently.  Acetaminophen is usually all that is needed for any residual discomfort. After a restful night, an ultrasound is performed to check on the babies and for any complications of the procedure.  Most patients are then given instructions on what to expect and then discharged to return home or to nearby temporary housing like the Ronald McDonald House, if home is far away. 

We ask all mothers to return to the CIFH several days after discharge for a follow-up ultrasound, an echocardiogram and a counseling meeting. During that visit, we will review the findings of the testing and what they tell us about the recovery from the procedure. Following that visit nearly all mothers are permitted to return home for the remainder of their pregnancy and deliver under the care of their primary obstetrician or maternal-fetal medicine (MFM) doctor. We ask all mothers to limit their activity to some extent for the remainder of the pregnancy. In most cases, these limitations are compatible with returning to work and the usual demands of parenting, etc. The details of the activity plan are individualized for each mother and will be discussed during every visit. 

What Are the Outcomes After Surgery for Twin-to-Twin Transfusion Syndrome?

Despite the serious nature of TTTS, the outcomes after surgery are very good in most cases. Our fetal surgeons have refined the approach over hundreds of cases and expect that 95% of the time after the operation at least one twin will survive, and greater than 80% of the time both twins will survive. Occasionally, one of the twins will not survive despite all of our efforts to prevent this from happening. Most often, this is due to insufficient development of the placenta prior to the procedure. Although a topic of intense research, there are currently no direct treatments for placental insufficiency.

Overall, the long-term neurologic outcome is  expected to be normal for 90% of surviving twins after surgery for TTTS. Of the remaining 10%, approximately half will exhibit mild (5%) or severe (5%) developmental delays. The biggest predictor of neurologic outcome is the degree of prematurity.  Therefore, all of our treatments are designed to minimize the risk for severe prematurity.

Apart from fetal loss and preterm delivery, major complications such as bleeding, blood clots, infection, recurrent TTTS or twin anemia polycythemia sequence (TAPS) are rare after an SFLP procedure. Ultimately, expert and timely care provides the best possible chance for a good outcome with each case of TTTS.

The later during pregnancy this condition develops, the better the prognosis is for both babies.