None — BACKGROUND: According to the American Pregnancy Association, twin to twin transfusion syndrome (TTTS) is a very serious disorder that occurs in identical twins. TTTS happens when the twin babies share blood vessels. As a result, one baby receives more blood flow while the other baby is deprived of blood flow. TTTS occurs about 15 percent of the time; however, fraternal twins do not face this risk due to the simple fact that they do not share a placenta. It is important to understand TTTS cannot be prevented. Some symptoms of TTTS are difference in umbilical cord sizes, difference in size between the two amniotic sacs, and evidence of fluid build-up. Additionally, if one baby is bigger than the other in the womb, this is also a warning sign. The pregnant mother should watch for noticeable signs in rapid growth of womb, abdominal pain, early and premature contractions, and early pregnancy swelling in hands and legs.
EARLY TREATMENT: Before technological advances and medical breakthroughs, the most common form of TTTS treatment was amniocentesis. With amniocentesis, excess fluid is drained, and the blood typically begins to flow normally again. Even then, this process is usually only 60 percent effective when it comes to saving the babies' lives. Septostomy is often performed if the amniotic fluid is drained. With septostomy, a small hole is made in the amniotic membranes. This procedure allows the amniotic fluids to even out in and rebalance for each baby. Unfortunately, many babies also lost their lives early on while still in the womb when amniocentesis was not used.
IMPROVED TREATMENT: Another treatment used for TTTS is laser surgery. With laser surgery, the blood vessels are sealed so that the blood cannot continue to pass through from baby to baby. With laser surgery, a scope is inserted through the mother's abdomen and into the twin's sac who is receiving more blood flow. Often, laser surgery completely restores blood flow, and both babies survive, in turn, eliminating TTTS. An advantage of laser surgery compared to amniocentesis is that amniocentesis may need to be performed multiple times throughout pregnancy, whereas laser surgery is typically a one-time event.
IN-DEPTH INTERVIEW WITH MICHAEL BEBBINGTON, M.D.
Michael Bebbington, M.D., MHSc, from Children's Hospital of Philadelphia, explains how a new laser surgery is helping twin babies before they're born.
Are we seeing a rise in the number of women having twins?
DR. BEBBINGTON: We are seeing a large increase in the number of twins being born largely as a result of increased use of reproductive technology.
Are a lot of those to older moms or younger moms?
DR. BEBBINGTON: It's across the board, but since more assisted reproduction is used by older moms, that's the group that ends up with more multiple pregnancies.
With a rise in the number of women having twins, you are also seeing a rise TTTS?
DR. BEBBINGTON: Well twin to twin transfusion syndrome, which is what TTTS stands for, is a complication that happens in a particular type of twins that are called monochorionic twins. This type of twins results from a splitting of a single embryo so they are commonly called identical twins. We know that those twins share a placenta and that there are connections between the blood supplies of the two fetuses within the placenta itself. The flow is normally balanced between the twins.
What becomes problematic then as they're developing?
DR. BEBBINGTON: In about 15% of cases, for reasons that we're not clear about, there becomes an imbalance in the exchange of blood. One twin starts to get more blood than its giving back. That twin becomes what we call a recipient twin and the co-twin then becomes the donor twin.
What happens at that point?
DR. BEBBINGTON: There's a very complex set of physiologic changes that takes place, as each of the twins adapts its physiology to changes in its blood volume.
What happens when you say they have to adapt?
DR. BEBBINGTON: The donor twin has a reduced blood volume and centralizes blood flow to its heart and its brain. There is less urine produced and the amount of amniotic fluid surrounding it goes down. Sometimes there is decreased growth, and sometimes we can see changes in the patterns of blow flow within the fetus that tell us that that twin could be in trouble. The recipient twin undergoes almost the opposite set of changes where it has a much increased blood volume and we see that the fluid around that twin starts to increase and that they undergo changes in the way the heart functions.
What are the changes?
DR. BEBBINGTON: The recipient twin, the twin that's getting the extra blood develops heart changes because the heart is working harder, We see that the muscle of the heart wall starts to thicken, that the valves that connect the pumping chambers from the reception chambers start to leak. The recipient twin can actually go into heart failure and die.
Is this something that can correct itself in the uterus?
DR. BEBBINGTON: Once the TTTS reaches a certain stage, no. Sometimes in the very early stages we can see fluctuations where it appears to resolve or it can just sort of hover in a very low grade problem. But generally, by the time people come to see us, it's already advanced to a stage that's not going to fix itself.
What are the options for families?
DR. BEBBINGTON: The best option that we have right now is laser therapy, which involves putting a scope into the uterus, into the sac of the recipient twin, tracing the blood vessels under direct visualization, and then using a laser to clot the blood in the blood vessels in the placenta that connect the twins.
What happens then to the fetuses? How does that differ after the surgery?
DR. BEBBINGTON: What the surgery does is really breaks the connections between the two fetuses, and so the transfusion stops, and then the physiology in the vast majority of cases reverses itself and they can go on and have a healthy, normal pregnancy.
Is there a timeframe within the pregnancy where this seems to develop?
DR. BEBBINGTON: TTTS can happen at any time during a pregnancy. Obviously the earlier it develops the more severe the problem. In terms of laser therapy, that's something that we can really only do between 17 and 26 weeks of pregnancy.
Why is that?
DR. BEBBINGTON: Because of technical limitations. After 26 weeks the blood vessels on the surface of the placenta get too large to laser. And also, when the pregnancy reaches a certain gestation, sometimes it's better for the babies to be delivered and put into the nursery rather than undergo surgery.
Without the surgical option, will these babies die?
DR. BEBBINGTON: The prenatal mortality rate without an intervention of some sort is about 85 to 90%.
Are there any other options other than surgical?
DR. BEBBINGTON: There is the option to do what's called an amnioreduction. This procedure essentially takes extra fluid out of the amniotic sac of the recipient twin and tries to bring that down to normal. Unfortunately what that does is really just treat symptoms. It doesn't treat the underlying connections or blood transfusion process, and so it's a less successful therapy overall.
How quickly do doctors have to intervene when this problem is detected? Can these babies go fairly quickly?
DR. BEBBINGTON: There's a great deal of variation in the speed with which the disease process can progress. Some, as I said, can be very slow and fluctuate. Others, in a matter of days, can go from very mild to very severe.
What happens with the remainder of the pregnancy then for the mom after this surgery? Is it a normal pregnancy after that?
DR. BEBBINGTON: Well after the surgery, it's never completely a normal pregnancy. All twin pregnancies need increased care. In the case of moms who have undergone surgery for twin to twin, they're seen weekly by their specialists for ultrasound follow-up to monitor the growth of the babies and the well-being virtually until they come to delivery.
Is this procedure done under general anesthesia? Is it a long procedure?
DR. BEBBINGTON: It's a procedure that we do under what's called conscious sedation. We give intravenous sedation for the mom, which also helps to keep the babies quiet during the surgery along with some local anaesthetic in the skin at the incision site.
What about risk to the mom?
DR. BEBBINGTON: Overall the procedure carries about an 18% risk of a complication that would result in the end of a pregnancy. There are small risks to every surgical procedure. The laser surgery for twin to twin doesn't carry any increased risks for mom.
How many of these TTTS cases are there nationwide? How common is this?
DR. BEBBINGTON: It's about 15% of monochromic pregnancies that will end up with twin to twin transfusion syndrome.
Could you just describe what a monochromic pregnancy is?
DR. BEBBINGTON: It's a special type of twins where the twinning has happened as a result of the splitting of one embryo. It happens at a certain point in time when the layers of the amniotic sac have not completely formed so that the babies are still in their own individual sacs, they're in amniotic sacs, but they have a common chorionic sac surrounding them.
You said TTTS can happen at any period of time. Usually what period of development? What gestation?
DR. BEBBINGTON: We see TTTS as early as 14 weeks and anywhere up to delivery.
How many cases a year?
DR. BEBBINGTON: I would say we evaluate somewhere in the area of about 250 to 300 sets of twins a year, not all of which come to surgery.
Do you think most people are surprised to hear that technology has advanced to that point?
DR. BEBBINGTON: I think most people are still very surprised at the extent of technological development that exists to allow us to intervene in a pregnancy while it's still in uterus.
What do you tell patients when they come in? How do you prepare families for what may be coming?
DR. BEBBINGTON: Families, when they come to see us, spend a day getting a very comprehensive evaluation, undergoing very detailed ultrasound evaluation and detailed echocardiography of both fetuses. They then have the opportunity to meet with either myself or one of my colleagues and we spend an hour to an hour and a half discussing the background of what's going on in the pregnancy, how this problem develops and the options that are available for therapy.
Are they able to leave with a sense of hope or optimism or in most cases is this not a good scenario?
DR. BEBBINGTON: I think most of our families leave with a sense of hope that we can actually do something to help a very complicated situation.
After these babies are born, will they have any health risks later on? Can you tell that they've even been through this kind of trauma early on?
DR. BEBBINGTON: In the vast majority of cases, when you look at children that are born that have been treated for twin to twin, they're completely normal, healthy children. We're still doing research on the long term outcomes. We are appreciating that in a very select number of cases, there can long term problems mostly related to preterm delivery. There may be potential long term cardiac complications, but that's still very preliminary in terms of research.
Is there anything you think people need to know?
DR. BEBBINGTON: I think one thing that we tell a lot of our families is that with laser therapy, the potential for a good outcome is very high. So when we start with a untreated prenatal mortality of 85%, our outcomes with laser therapy are an overall survival of about 86% with survival of at least 1 of the 2 in 92% and survival of both twins in 74%.
In terms of seeing an increase in the number of people, is that an increase over say five years ago?
DR. BEBBINGTON: Absolutely. It's definitely an increase. As people are getting more aware of the diagnosis and with use of early ultrasound, the diagnosis is being made earlier on and hopefully at point where treatment is easier.
Is there any way that a woman can tell that there's a potential problem?
DR. BEBBINGTON: Really, the only thing that most mothers are aware of is that their abdomens increase in size very rapidly, and that should trigger them to get to see their doctors to have an ultrasound evaluation to see if there's a problem.