Laser for Twin-Twin Transfusion Syndrome (TTTS)

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What is Twin-Twin Transfusion Syndrome (TTTS)?


Twin-twin transfusion syndrome poster presentation (click to enlarge)

TTTS poster

Twin-twin transfusion syndrome (TTTS) is a rare syndrome that only occurs in monochorionic (identical) twin pregnancies, where two fetuses share a single placenta. Both fetuses are connected by blood vessels (anastomoses) on the placental surface. As a consequence, these fetuses continuously exchange blood. TTTS is largely due to an imbalance in the exchange of blood through these anastomoses. In 85-90% of cases, the transfer of blood from one fetus to the other is balanced and each receives a similar quantity of blood as it gives away. In about 10-15% of cases however, this exchange of blood is imbalanced and one fetus (the recipient, often called “Poly”) receives more blood than it gives away. The other fetus (the donor, often called “Oli”), gives away more blood than it receives. The recipient fetus will become volume overloaded, and will try to get rid of this extra fluid by urinating. As a consequence, its bladder will become very full and this fetus will produce too much amniotic fluid (polyhydramnios). The volume overload will often also be reflected in early signs of heart failure. The donor fetus on the other hand will try to preserve all its fluid and will stop urinating. Its bladder will usually be empty and the fetus will have too little amniotic fluid (oligohydramnios). On ultrasound, the fetus is usually seen enclosed in its membranes like shrink wrap. TTTS can be diagnosed on ultrasound as a severe discordance in amniotic fluid between the two fetuses.

What is the outcome of Twin-Twin Transfusion  Syndrome?

Twin-twin transfusion syndrome typically occurs between 16-26 weeks gestation. When left untreated, the water may break too early leading to a very premature birth (often before fetal viability). Sometimes, the recipient fetus can also die in-utero due to heart failure. Some survivors may have some kind of long-term disability.

What other tests should we consider?

When TTTS is suspected, or severely discordant amniotic fluid is seen, a detailed ultrasound at a specialized center such as the Fetal Medicine Unit at Mount Sinai Hospital is required. This allows us to differentiate TTTS from other complications of identical twin pregnancies and to evaluate the impact of TTTS on each fetus.

What therapy is available?

Until the mid 1990’s, TTTS could only be treated by removing the excessive amniotic fluid from the recipient’s sac by repetitive amniotic fluid drainage, through a needle inserted into the uterus. Therapy has now shifted to fetoscopic laser ablation (blockage) of the communicating placental vessels. This therapy, which targets the underlying cause of TTTS (the placental blood vessels), results in higher survival rates, more advanced gestation at delivery and better infant outcomes than repeated amniotic drainage in a large study. Amniotic fluid is also removed (through the same needle) at the end of the laser procedure, some of which is usually sent to test the chromosomes. The laser procedure is done under light sedation, which is the safest method for the mother, and her partner, or a companion, can be present during the procedure. The mother will be kept very comfortable during the surgery.

After laser surgery is completed, the donor fetus can start urinating again and will refill the amniotic fluid in its sac. Simultaneously, but over a longer time frame, the heart function in the recipient fetus can recover. Despite the laser treatment, one fetus dies in about 15% of cases. This is usually due to unequal sharing​ of the placenta (sIUGR: selective intra-uterine growth restriction). In about 20% of cases, both twins will still be delivered very early and may not survive. Overall, both fetuses will survive in about 50-60% of cases and at least one fetus will survive in 80-90%. The average gestation at delivery after fetoscopic laser is 33 weeks. The risk for developmental delay in survivors is approximately 8-12%. This is mainly related to an early gestational age at delivery (prematurity) and cannot be predicted at the time of laser. Long-term kidney function in the donor and heart function in the recipient are both normal in the majority of cases. Recipient fetuses are at a slightly higher risk of having heart defects (such as a narrow pulmonary valve).

 

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