When Two or More Babies Share a Placenta?
Twin-to-twin transfusion syndrome, or TTTS, is a disease of the placenta. It can affect identical twin pregnancies or higher order multiple pregnancies in which two or more of the babies are monochorionic, or share a placenta.
In TTTS, blood passes disproportionately from one baby to the other via connecting blood vessels within their shared placenta. This means that one baby, the recipient twin, gets too much blood, while the donor twin doesn’t get enough blood, putting both at risk for serious injury or death.
“We know that in pretty much every monochorionic pregnancy there are vascular communications between the twins,” says Dr. Francois Luks of the Brown University Fetal Medicine Program. “In about 20 to 25 percent of these pregnancies, some degree of TTTS occurs. In about 10 to 15 percent, it’s severe.”
Both twins try to adapt. The donor twin’s body works to conserve fluid and energy, leading to oligohydramnios, or low amniotic fluid, and intrauterine growth retardation, or IUGR. As the condition worsens, the donor twin’s fluid output may become so low that he or she is literally “stuck” to the side of the uterus.
The recipient’s body tries to get rid of the excess fluid by increasing urination, which leads to polyhydramnios, or excess amniotic fluid. The recipient is also dealing with an excess of blood cells, leading to complications of increased blood volume and abnormal blood thickness, or hyperviscosity.
And as the recipient puts out more and more fluid, the uterus begins to stretch dangerously, and pressure is put on the mother’s cervix, often leading to preterm labor and premature rupture of membranes. Both donor and recipient are likely to be very fragile and have a tough time coping with the demands of prematurity.
TTTS is diagnosed via ultrasound, although some mothers may notice symptoms such as fatigue, pressure in the belly or back and a sudden increase in the size of their abdomen. A staging system is used to diagnose the severity of the disease and to determine treatment. Stage I is the least severe form of TTTS, and Stage V is the most severe.
What Goes Wrong?
We don’t know exactly why TTTS occurs in some monochorionic pregnancies, Dr. Luks says. It was once believed that when monochorionic twins had a lot of vascular communication through the placenta, they would balance each other out, and when they didn’t, they would have a higher risk of developing TTTS. However, that’s not necessarily true.
“What we do know is that the diameter and the flow through each vessel probably matters a lot,” Dr. Luks says. “So if you have one fairly large vessel with a high flow of blood from one to the other, that’s probably going to be the one that is going to cause TTTS.”
Hormonal factors may play a part in the disease’s progression as well, Dr. Luks says. “If you lose blood, for instance, your body will start secreting certain hormones to make sure that you conserve fluid and conserve urine, so that you don’t become hypotensive,” he says. “And if you consume too much fluid, or if you get too much fluid through an IV, the opposite is going to happen. Hormones will regulate that as well.”
In TTTS, the donor twin is losing a lot of blood to the recipient twin, so his hormones kick in to try to conserve as much fluid as possible. Unfortunately, those hormones will also cross to the recipient twin, causing the recipient to retain even more fluid. More research is needed in this area, Dr. Luks says, and more is being done.
Without treatment, the chances of both twins surviving severe TTTS is as low as 10 percent, and the chances that one will survive hover around 30 percent. Thankfully, the last 20 years have seen huge advances in treatment options.
There are two main treatment options for TTTS. In amnioreduction, excess fluid is removed from around the recipient twin. The reason this works isn’t entirely clear, but it is believed that removing the excess fluid decreases the risk of rupture of the membranes and preterm labor, and may help reduce pressure on the umbilical cord of the recipient twin, thus improving blood flow between the recipient and the placenta.
But amnioreduction isn’t a cure for TTTS – it only reduces some of the effects. The fluid is likely to build up again, and the procedure will need to be repeated. Each time, the risk of bleeding, infection or ruptured membranes goes up.
Laser coagulation of the communicating placental vessels is a form of fetal surgery. First performed in 1995, laser coagulation actually stops TTTS by using a laser (inserted endoscopically into the uterus) to seal off the blood vessels that are allowing transfusion from one twin to the other. The procedure does have risks to both mother and fetuses, and until recently, there was no proof that laser coagulation was superior to amnioreduction.
However, in 2004, the Eurofoetus study, a randomized, controlled trial overseen by European researchers, showed that laser coagulation did lead to better outcomes than amnioreduction for advanced TTTS.
There are many factors that influence how TTTS will be treated in any given case, Dr. Luks says. First is the severity of the disease at the time of diagnosis. “If it presents in Stage III or Stage IV, at that point it’s pretty much a given that the only thing that can help, if anything at all, will be the laser,” he says.
But if TTTS is found in a lesser stage, such as Stage I, there is a decent chance that the syndrome will not get worse, but in fact will remain stable or improve, Dr. Luks says. “But there is also a risk that it could worsen,” he says. “That’s the one thing that we don’t have a handle on yet – if you are diagnosed with Stage I, it is impossible to predict, ‘Well, you are going to be Stage II or Stage III by next week. Or in two weeks. Or in two days.’ That we can’t do. We’ve seen all possible combinations.”
In addition, if TTTS occurs after the point when the babies would be viable outside the womb (around 25 to 28 weeks gestation), it is often safer to focus on therapeutic measures and early delivery, Dr. Luks says.
Other factors that can affect treatment include cervical length, placental location and prior amnioreductions, says Dr. Ruben Quintero, professor and director of the Division of Maternal-Fetal Medicine at the University of South Florida College of Medicine. Triplets can also make surgery more difficult.
“The single most important message is that TTTS can be treated effectively today,” says Dr. Quintero, who was the developer of the TTTS staging system. “Our current numbers show at least one fetus surviving in approximately 90 percent of patients, and two surviving fetuses in approximately 75 percent of patients. Although there can still be important complications, particularly resulting from prematurity, the overall prognosis for patients treated with the selective laser technique developed by us is extremely good.”
Dealing with the Diagnosis
After a diagnosis of TTTS, one of the first issues families struggle with is hope, says Lonnie Sommers, president, executive director and founder of the Fetal Hope Foundation. “There’s a lack of information and awareness out there even in the medical community,” Sommers says, with even many health care providers unaware of the tremendous advances made in TTTS care over the past 15 years.
Sommers speaks from personal experience. In 2003, he and his wife were expecting identical twins. During what they thought would be a routine ultrasound at 20 weeks, they found out that their babies were girls – and that they were suffering from severe TTTS. The Sommers were told that the babies would likely live only a few more weeks, and that while they could try to save them, the best option might be to terminate the pregnancy.
It was an information packet from the Twin-to-Twin Transfusion Syndrome Foundation that gave the Sommers the information they needed to find a specialist that could help them. Within days, they were on their way to see one of the world’s top TTTS experts, and a decision was made to perform laser surgery. Both girls survived, and today are thriving 3-year-olds.
“The first thing families want to know is, ‘What can we do?'” Sommers says. “I think that what is helpful to them is, first and foremost, to seek out resources that can help them, such as the Fetal Hope Foundation and the Twin to Twin Transfusion Syndrome Foundation. That’s the first thing: being able to speak with somebody that’s been through it, and can kind of help them along, help them understand their particular case better.”
The next issue families struggle with is coming up with a plan of action. Because there are different viewpoints on how to treat TTTS, families usually need to talk with at least a few experts to help them make decisions on care. “We try to help them get in touch with experts quickly, and try to help them understand things from a less clinical standpoint,” Sommers says.
If Sommers could say one thing to families put in the same situation as he and his wife were three years ago, what would it be? “I want them to know there is hope,” Sommers says. “There have been so many advances in treatment, so while unfortunately not every situation ends up with a happy ending, there are things that can be done. There is hope.”