WEDNESDAY, July 7, 2004 (HealthDayNews) -- Like everything else they have in common, identical twins usually share the blood supply within the womb, but a rare condition throws this division of nutrients off balance, threatening the survival of one or both twins.
In the past, there was little doctors could do to improve the odds in these cases. But the advent of intrauterine laser surgery may be changing all that.
The results of a new multinational European study "suggest that laser may improve the chance of at least one baby surviving and reduce brain injury, at least in advanced-stage cases," said Dr. Nicholas M. Fisk of Imperial College London, co-author of a commentary on the study appearing in the July 8 issue of the New England Journal of Medicine.
In twin-to-twin transfusion syndrome -- which occurs in about one in every 2,700 pregnancies -- identical twin fetuses subsist unequally from the same placenta. In this environment, the dominant fetus grows larger while the weaker one remains smaller and undernourished. The larger fetus also excretes more urine, putting pressure on the smaller fetus as the volume of amniotic fluid around the larger twin expands.
If left untreated, twin-to-twin transfusion syndrome poses serious dangers for both fetuses. According to Fisk, just "20 percent of babies will survive, around a quarter of whom may have serious brain injury."
Advances in maternal-fetal medicine have given obstetricians new weapons to fight the syndrome, however. The most common intervention, serial amnioreduction, involves a periodic drainage of excess amniotic fluid from the womb at different points in the pregnancy, to reduce intrauterine pressure.
"This reduces the risk of preterm labor, is curative in about 20 percent of cases, and has a baby survival rate of 60 percent," Fisk said. However, the technique is generally considered ineffective in more advanced cases.
The advent of endoscopic laser surgery has recently provided doctors with a second option. With this technique, surgeons introduce a video-equipped laser into the womb, using it to surgically correct those blood vessel abnormalities that allow one twin to take the lion's share of the placental blood supply.
In their study, a team of French researchers led by Dr. Marie-Victoire Senat of University Paris-West Versailles-St. Quentin compared the survival of 72 pairs of twins threatened by twin-to-twin transfusion and treated with either serial amnioreduction or laser surgery.
They found that, especially for cases diagnosed before 26 weeks gestation, laser surgery "is a more effective first-line treatment than serial amnioreduction."
While 56 percent of twins treated with amnioreduction were delivered successfully and lived to at least four weeks after birth, that number rose to 76 percent for twins treated with laser surgery.
Laser-treated twins also had a much lower rate of neurological damage compared to those treated with amnioreduction (31 percent vs. 52 percent, respectively).
Fisk agreed that laser surgery has greatly improved the survival chances of twins threatened by this syndrome. "Its advantage is that it can cure even severe disease and protect the baby from impaired blood flow to the brain, thereby reducing brain damage in severe cases," he said.
On the other hand, he cautioned it may be too early for laser surgery to become the method of choice in all cases of twin-to-twin transfusion syndrome. Only a few highly skilled surgeons in developed countries currently have the training to perform this type of delicate laser procedure, he pointed out, and the procedure is not without risk.
"It's difficult to be sure that one is destroying only abnormal vessels and not any normal placental vessels," Fisk explained. In fact, laser surgery "sometimes leads directly to the death of one or both babies," he said.
For these and other reasons, Fisk believes more studies need to be done before laser surgery is declared the gold standard for all cases of twin-to-twin transfusion syndrome. A final answer on which method works best may not be far off, though. A National Institutes of Health funded, randomized trial of these two therapies is currently under way, he said.
For information on a range of issues surrounding pregnancy, visit the American Pregnancy Association.