What is twin-to-twin transfusion syndrome (TTTS)?
TTTS is a syndrome that affects the structure of the placenta. The placenta is an organ that forms during pregnancy, attaching to your uterus and providing blood and nutrients to your baby. In TTTS, there is an intrauterine blood transfusion from one fetus to the other.
There are many blood vessels in the placenta. In TTTS, abnormal blood vessels form in the placenta, and blood flows unevenly between the fetuses. TTTS leads to unequal placental sharing, which means that one baby receives more blood than the other.
This condition affects pregnancies with identical twins who share a placenta or multiples with more babies, such as triplets. As a result, one of the twins becomes a “donor,” and the other twin becomes a “recipient” of this twin-to-twin transfusion.
How does TTTS affect a fetus?
TTTS can affect both twins negatively. It is a progressive condition that worsens throughout the course of the pregnancy.
The donor twin receives insufficient blood, oxygen, and nutrients. This twin develops anemia, a condition characterized by a low amount of red blood cells and hemoglobin. The anemic fetus prioritizes vital organs like their brain and heart, and less vital organs become atrophied or damaged. These organs include the donor’s kidneys, and so the fetus produces less or no urine. This leads to low levels of amniotic fluid.
The donor baby also becomes dehydrated and grows more slowly. The donor twin usually has 20 percent less birth weight than the recipient twin. The donor twin’s hemoglobin may be 5 g/dL less than the recipient’s.
TTTS can affect both twins negatively. It is a progressive condition that worsens throughout the course of the pregnancy.
The recipient twin, on the other hand, has to deal with an abnormally high blood flow. They grow larger in size and urinate constantly, leading to excessive amniotic fluid. The recipient’s blood becomes abnormally thick, and they can develop heart failure as a result. This can lead to hydrops fetalis, a condition characterized by generalized edema (accumulation of fluid).
Since the recipient twin’s circulation depends on their twin’s blood flow, they face an increased risk of death or serious injury if their twin dies. Even if both twins survive, they have a high risk of brain ischemia (insufficient blood flow) and other neurologic and pulmonary complications.
Understanding Quintero staging system
The Quintero staging system can help your doctor assess the severity of your babies’ TTTS. This system helps provide an estimate of the condition’s severity and progression throughout your pregnancy.
The five stages of the Quintero TTTS staging system are:
- Stage I — Imbalanced amniotic fluid in each sac. In most cases, the twins are very different in size.
- Stage II — The donor twin’s bladder can’t be visualized or isn’t filled with urine for at least 60 minutes.
- Stage III — Signs of abnormal blood flow are seen in the umbilical cords or hearts of one or both fetuses.
- Stage IV — One or both twins show signs of heart failure, such as hydrops.
- Stage V — Death of one or both twins
TTTS risk factors
The only known risk factor of twin-to-twin transfusion syndrome is being pregnant with identical twins. All twin pregnancies that share a placenta have a 5–38 percent chance of developing TTTS; however, the condition occurs randomly.
Causes of TTTS
The reason TTTS occurs is something called placental vascular anastomoses, most commonly deep artery-to-vein anastomosis. The underlying causes of anastomosis formation is unknown. TTTS occurs spontaneously usually between weeks 16 to 25, and it is not known whether it is hereditary.
TTTS diagnosis
A doctor can diagnose twin-to-twin transfusion syndrome during an ultrasound, particularly during the second trimester. Since we don’t know what causes TTTS or how to prevent it, it’s very important to attend all your scheduled prenatal care appointments.
A doctor can diagnose twin-to-twin transfusion syndrome during an ultrasound, particularly during the second trimester.
If your doctor identifies signs that could point to TTTS, such as twins with different sizes or imbalanced amniotic fluid levels, you’ll probably be scheduled for more-frequent ultrasounds. This can help your doctor determine whether your babies have TTTS and follow the progression of the disease.
Other prenatal testing procedures might be suggested to confirm the TTTS diagnosis and rule out other abnormalities.
Ways to treat TTTS before birth
The best treatment course for TTTS will vary depending on the severity of each case and the overall health of the mother and her babies. Fortunately, there are many different treatment options for twin-to-twin transfusion syndrome.
In most cases, you’ll be prescribed bed rest for the remainder of your pregnancy. You’ll also need to get frequent ultrasounds, and you might also require nutritional supplements. Fetal MRIs and echocardiograms will determine your babies’ well-being.
Delivery
In severe cases, or if TTTS is diagnosed later in the pregnancy, delivering the twins might be the best option. The best time to deliver babies with TTTS will depend on many individual factors. Your medical team will probably try to deliver the babies as far into the third trimester as possible.
This, of course, will depend on your babies’ health and development. In some cases, continuing a pregnancy with TTTS might be riskier than the consequences of preterm birth.
Amnioreduction
Amnioreduction is less invasive than other TTTS therapies, but it might not be the most effective solution for all cases. During this procedure, excess amniotic fluid is removed from the recipient twin’s amniotic sac to relieve pressure.
Amnioreduction is less invasive than other TTTS therapies, but it might not be the most effective solution for all cases.
Studies have found that this procedure has a greater possibility of success when a superficial anastomosis is found between the twins, and TTTS is detected at a lower stage.
Sometimes it needs to be performed several times during pregnancy.
Fetoscopic laser photocoagulation
This type of TTTS surgery uses a laser to eliminate the abnormal blood vessels that connect both twins. This is done by introducing a thin scope through the mother’s abdomen and into the uterus. Then the scope is used to examine and identify abnormal blood vessels, and the laser beam destroys them.
Fetoscopic laser photocoagulation is widely considered to be the most effective treatment for TTTS. It is a highly specialized procedure that is performed in only a few centers around the world.
Through this procedure, the placenta is functionally separated and TTTS is eliminated. After the blood vessels are removed, an amnioreduction is usually performed to further improve the outcome. After this procedure, the survival rate for both twins is approximately 75 percent and 85 percent for one twin.
Fetoscopic laser photocoagulation is widely considered to be the most effective treatment for TTTS. It is a highly specialized procedure that is performed in only a few centers around the world.
Cord Coagulation or occlusion
Cord coagulation or occlusion is a procedure used to selectively terminate one of the twins. This is a very difficult decision to make, but it can maximize the chances of delivering one healthy baby.
During this procedure, a needle is inserted into one of the twins’ umbilical cords, and the blood flow is coagulated. As a result, the remaining twin will continue to develop normally without suffering the negative effects that would come from their twin’s spontaneous death. This procedure, although not ideal, can be the best option for pregnancies where one of the fetuses is too weak or sick and can’t be delivered safely.
Ways to treat TTTS after birth
If left untreated, the twin-to-twin syndrome survival rate is very poor — approximately 10–15 percent. Even if both babies are delivered, the mortality rate of severe TTTS is 60–100 percent, and there’s also a very high risk of neurologic injuries.
The treatment for TTTS twins after delivery will largely depend on their specific health problems. It’s very common for TTTS babies to require care in the neonatal intensive care unit after being delivered.
If left untreated, the twin-to-twin syndrome survival rate is very poor — approximately 10 to 15 percent.
However, most twins who receive TTTS treatment during pregnancy and are delivered safely go on to be healthy children. Babies who are born prematurely or have low birth weights have a higher risk of long-term health problems, such as cerebral palsy, vision problems, and hearing loss.
The chance of TTTS in future pregnancies
Since TTTS doesn’t have a genetic cause or associated risk factors, the probability of developing TTTS in a future pregnancy is always the same as it was before. This probability is approximately 1 in 1,000 identical twin pregnancies. However, it’s extremely uncommon for a woman to get pregnant with identical twins twice — 1 in 70,000 pregnancies!
Since TTTS doesn’t have a genetic cause or associated risk factors, the probability of developing TTTS in a future pregnancy is always the same as it was before.
Twin-to-twin transfusion syndrome is a very complicated medical condition, and it can be a heartbreaking diagnosis. However, detecting the disease early and getting the best possible treatment can improve your babies’ chances of being born healthy and growing up without complications. Just like with any other pregnancy-related condition, it’s very important to attend all your prenatal checkups to ensure that your babies are developing correctly and treat any problems that might arise.
