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About Twin-to-Twin Transfusion Syndrome

Twin-to-twin transfusion syndrome (TTTS) may sound like a plot from a science fiction movie, but it's an actual phenomenon that can occur during a twin pregnancy. Undetected or untreated, it can have devastating consequences for the babies. However, new treatment options give doctors the ability to correct the situation and offer new hope to parents impacted by the disease.

Essential

The effects of TTTS can produce a great deal of variability in the appearance of monozygotic or "identical" twins. The donor twin is usually much smaller and paler, while the recipient twin is larger with a ruddier complexion.

What Is It?

TTTS, also known as feto-fetal transfusion syndrome or stuck twin syndrome, is a disease of the placenta. It doesn't make the mother sick, and its effect on the babies is environmental, not direct. In other words, the babies will begin to develop perfectly normally, but because the placenta they depend on to supply oxygen and nutrition malfunctions, they risk heart failure, brain trauma, and damage to their organs.

The placenta circulates blood and nutrients from the mother to her babies. Within a shared placenta, blood vessels called chorioangiopagous vessels may develop, connecting the circulatory systems of both babies via the placenta. This causes an unequal exchange of blood flow between the babies. Essentially, one fetus becomes a donor, pumping blood into the second, recipient fetus. This situation causes problems for both babies, with the donor twin not getting enough blood and the recipient receiving an excess.

The donor twin is at risk for anemia, intrauterine growth retardation, and restricted amniotic fluid (oligohydramnios). While the donor's growth is stunted, the recipient twin grows larger and larger. The extra blood overloads his circulatory system and puts him at risk for heart failure. As he struggles to process the extra blood, his urine production results in an excess of amniotic fluid (polyhydramnios). Eventually, polyhydramnios can trigger the onset of preterm labor and both babies are at risk of being born too early to survive outside the womb.

E Fact

As the amount of fluid surrounding the recipient twin increases, the donor twin may be pushed to one side of the uterus. As her fluid levels decrease, she may appear to be stuck to the wall of the womb. Thus, the term "stuck twin syndrome" has been used to describe this condition.

The timing of the disease ultimately determines the prognosis for the babies. It is easier to overcome later in pregnancy, when the simplest solution is to deliver the babies. Although they may face the consequences of a premature birth, they will escape the threat to their survival that exists if they remain in the womb. However, if the onset of TTTS occurs earlier, before the babies are viable, the situation is more dire, although there are treatment options. There are five stages of TTTS:

When TTTS is detected in the second trimester, it is usually termed chronic or severe. After twenty-four weeks, it is defined as moderate. When it occurs later in the third trimester, it is labeled mild or acute.

Who Gets It?

Not all twins are at risk for the condition. It only affects a percentage of monozygotic twins, those individuals resulting from one egg. Depending on when the egg splits and implants, monozygotic twins may develop individual placentas or share a single placenta. TTTS only occurs when there is a single, shared placenta.

The term monochorionic describes twins that are joined in a single chorion, the membrane that attaches to a single placenta. Only monochorionic twins are at risk for TTTS because they are the only type whose circulatory systems may connect through the placenta. Although there has been some speculation that two fused placentas could develop a circulatory connection susceptible to TTTS, researchers of the disease confirm that it is simply not feasible.

E Alert

TTTS only affects monozygotic twins. It occurs in about a third of monochorionic pregnancies, or less than 10 percent of all identical twins. If untreated, it has as much as an 80 percent fetal mortality rate.

How Is It Diagnosed?

One of the reasons that a multiple pregnancy is subjected to closer scrutiny is so TTTS can be detected. Doctors use ultrasound to assess the risk by determining the number of placentas. If there is just one, subsequent ultrasounds will follow the babies' growth and development, as well as the amount of amniotic fluid, to confirm that it remains equalized. If a discrepancy develops, further ultrasound testing may reveal the presence of too much or too little amniotic fluid around each baby, a sure sign that a shared circulatory connection is shunting blood between the babies.

What Can Be Done?

In past times, babies affected by TTTS were doomed. Without ultrasound technology to detect the disorder, it was likely that one or both of the babies would die in utero, or that they would be born too early to survive. Now, not only does sonography enable doctors to diagnose the condition, new treatments allow it to be cured.

Up until very recently, the primary treatment approach was to stave off preterm labor until the babies were viable and could be delivered. This was accomplished by draining the excess fluid surrounding the recipient twin. Amnioreduction, a procedure similar to amniocentesis, was performed at regular intervals to remove fluid from the recipient baby's amnionic sac. While it is generally effective in stabilizing the situation, it carries the same risks as amniocentesis, including infection and miscarriage. It also does not compensate for the damage occurring to the donor twin.

In the 1990s, Dr. Julian DeLia developed an amazing procedure that allows doctors to correct TTTS by using a laser to seal off the connections in the placenta. The procedure is performed while the babies are still in utero, using a fetoscope, a powerful telescope allowing a surgeon to see inside the womb through a tiny incision. A 2004 study confirmed that this procedure, fetoscopic laser coagulation, produces a better outcome for the babies.

Treatment for TTTS depends on how far along you are in your pregnancy, and to which stage the disease has progressed. Fetoscopic laser surgery is available in half a dozen facilities in the United States as well as other locations in Australia and Europe. As studies confirm its success in treating TTTS, it will become more widely available in the next few years.

From The Everything Twins, Triplets, and More Book Copyright © 2005, F+W Publications, Inc. Used by permission of Adams Media, an F+W Publications Company. All rights reserved.

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