The use of lasers in fetal surgery may become more widespread, if Dr Ruben Quintero of the Florida Institute for Fetal Diagnosis and Therapy in Tampa, Fla., has his way. Quintero successfully separated the cardiovascular systems of two identical fetuses that were sharing the same placenta and outermost natal sac but receiving unequal proportions of blood.
Known as twin-twin transfusion syndrome (TTTS), this condition occurs when the veins and arteries in the shared placenta are situated in such a way that the amount and direction of blood flow favors one fetus over the other. Typically, one twin becomes large and swollen with excessive amounts of amniotic fluid while the other shrinks and receives little or no fluid. In severe cases, both the recipient twin and the donor twin face mortality rates of nearly 100 percent. TTTS occurs in approximately 10 percent of pregnancies in which identical twins share the same outermost natal sac, or chorion.
Using a 1064 nm Nd:YAG laser from Surgical Laser Technologies of Montgomeryville, Pa., Quintero cauterized selected blood vessels that communicated between the two fetuses. (Other vessels, such as those carrying essential nutrients and oxygen, were left intact.) With the offending vessels shut off, the chances for survival improved to an 80 percent chance of one twin surviving and a 50 percent chance of both twins surviving. In this case, both twins were born alive.
While the procedure has been done previously (see "Laser can increase fetal survival in identical twins," Biophotonics International, July/August 1998, pp. 60-61), Quintero used a different method to determine which vessels to seal off and which to leave alone. Where others had used the membrane dividing the two fetuses as a landmark, he instead traced and mapped each blood vessel from placenta to fetus to determine its function. Quintero said that while the dividing membrane will be located halfway between the two fetuses in normal twinning, in TTTS this membrane will be off-center and hence flawed as a landmark. He commented, "The landmark that divides your yard from your neighbor's yard may be a fence, but just moving the fence one way or the other doesn't change the boundary. The landmark is totally arbitrary. The same thing happens in the placenta with the dividing membrane."
Quintero said he hopes to simplify his technique and promote it as a reliable, more reproducible procedure for others to follow. Surgeons operating in the womb currently face many difficulties: fetal flesh is not as sturdy as that of a fully formed human being, and just the experience of surgery can cause the fetal brain to bleed uncontrollably. In addition, surgeons have to make sure they do not accidentally trigger premature delivery, as the smallest gap between the amniotic sac and the inner wall of the uterus tends to enlarge and trigger preterm labor.
Accordingly, he's trying to promote the laser-based procedure through the establishment of a series of regional centers. He said, "Parents should not have to travel all the way from Alaska to Florida for fetal surgery."
-- Dan Drollette
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