Laser ablation of placental anastomoses was pioneered in the US and has been performed for over 10 years in North America and and Europe. The procedure aims to treat the underlying cause for TTTS by coagulating the vascular anastomoses with a laser beam.
Ultrasound is used to identify the placental cord insertion of each baby (colored points).
A large needle in a hollow tube (sheath) is directed by ultrasound into the amniotic sac of the recipient twin. The needle part is withdrawn and an optical instrument like a miniature telescope (called a fetoscope) is passed through this sheath. The fetoscope is used to visualize the connecting vessels. A laser fiber is also passed down the sheath, and the vessels are then coagulated (sealed shut) with the laser. Coagulating the vessels stops the blood flow between the donor and the recipient within the placenta. The coagulation is done on the surface of the placenta, in the territory between the twins, where the imbalanced blood volume sharing takes place. The umbilical cords themselves are not interfered with.
An advantage of this therapy is treatment of the underlying cause with a single procedure. Following the closure of all connecting vessels during the procedure both twins have a chance for subsequent normal development. One limitation is that it is available in only selected centers worldwide. Insertion of the fetoscope may result in rupture of membranes, preterm labor and infection, in up to 10% of patients. There is also a small risk that perforation of small blood vessels in the abdominal wall or on the uterus results in maternal bleeding. Injury to the uterus may require cesarean section or in rare circumstances hysterectomy (removal of the uterus). There is also the theoretical risk of injury to other abdominal organs of the mother, including the bowel, which then may require surgical intervention, and opening of the abdomen. The overall risk for these complications is approximately 1-2%. For prevention of infection and preterm delivery intravenous antibiotics and magnesium as well as oral indomethacin are given on the day of surgery and the following day. Indomethacin is an anti-inflammatory agent used in rheumatoid arthritis, which has excellent success at stopping preterm labor.
After successful treatment, the donor bladder begins to fill (small black circle in the middle of the abdomen) and the blood flow in the umbilical cord improves (right image).
On the recipient side, there is gradual improvement in heart failure from the abnormal tracing before the laser treatment (part of the blood flow in the heart cycle runs backwards, on the left) to normal cardiac function with all blood flow forward (on the right).
To date approximately 1000 procedures have been performed in five major European centers as part of a collaborative trial (Eurofetus project). Results published after the first 220 procedures show the chance for survival of both twins is 55%, survival of at least one twin is 82% and the risk for loss of both twins is 18%. Some increased risk for neurological damage in surviving babies remains, but is significantly lower than the risk following serial amnioreduction (less than 9%). These data reflect initial results and will tend to improve with experience.
There are several factors that can make the procedure less successful, including :
- Anterior placenta (harder to visualize with the 'scope inserted in the mother's side)
- Later gestational age (our cutoff is 26 weeks gestation. After that, the particles in the amniotic fluid may make it impossible to do a safe procedure.)
- Cervix is already dilated or mother in true preterm labor
- Previous amniodrainage. This makes fetoscope insertion dangerous and allows the placenta to fold up, hiding the anastomoses we must visualize to coagulate.
These are relative problems with laser ablation. It remains the best chance of having two healthy surviving babies delivered near term.