What is TTTS?
Twin-twin transfusion syndrome (TTTS) is a problem where one fetus — the donor twin — pumps blood to the other fetus — the recipient twin. The condition occurs in about 10 percent of all pregnancies where identical twins share a placenta. That amounts to about 2,000 patients per year in the U.S.
Without intervention, the recipient twin receives too much blood and may develop fluid overload, heart failure, and die, and the donor twin may die from not having enough blood (severe anemia).
Almost all identical twins exchange blood across the placenta, although usually the exchange is balanced. In TTTS, the blood connections in the placenta are abnormal and the blood passes unequally between the two fetuses. TTTS occurs in varying stages of severity, which may or may not progress to the point where intervention is needed.
Twin-Twin Transfusion Syndrome (TTTS) | Symptoms & Causes
What are the symptoms of TTTS?
Symptoms of the recipient twin:
- very large amount of urine in the bladder
- too much amniotic fluid in the sac (polyhydramnios)
- larger than the donor twin and possibly swollen with too much blood
- congenital heart failure from an excess of blood
Symptoms of the donor twin:
- little or no urine in the bladder
- too little amniotic fluid in the sac (oligohydramnios)
- much smaller than the recipient twin
What causes TTTS?
The exact cause of TTTS is unknown. There are several variations of blood vessel development that may lead to unbalanced blood exchange. In addition, the fetus's response to altered blood volume may worsen the condition.
Twin-Twin Transfusion Syndrome (TTTS) | Diagnosis & Treatments
How is TTTS diagnosed?
Signs of the condition may be noted on a routine prenatal ultrasound, or your obstetrician may refer you for an ultrasound if your uterus measures larger than it should for your particular week of pregnancy. The discrepancy in measurement doesn't always mean that there is a problem.
But if a problem is suspected on the ultrasound, you may be referred to another doctor who specializes in high-risk cases for a more detailed Level 3 ultrasound.
Other tests you may encounter include:
- Fetal echocardiography: A special ultrasound of a baby's heart.
- Doppler flow study: This lets your doctor assess blood flow in the umbilical blood vein and arteries, fetal brain and fetal heart.
- Magnetic resonance imaging (MRI): To determine if there is any neurological damage in the donor twin; it takes pictures of the fetus's brain through the mother's abdomen
Ultrasound findings that point to a diagnosis of TTTS include identical twins with a shared placenta and abnormal communicating blood vessels. You may also hear the term "stuck twin," which refers to the donor twin, who, with such little fluid in the sac, is restricted in movement and can become stuck against the uterus.
When one twin dies there is a serious risk of death or severe neurological injury to the other fetus. Without treatment, death will occur in about 80 percent of these cases.
How do we treat TTTS?
There are several different procedures used to treat TTTS. Which procedure or combination of procedures is used will usually depend on the level of severity of the condition.
Some cases of TTTS never progress past the earliest stages, when there is still urine in the bladder of the donor twin, who never becomes "stuck." These cases would require only close monitoring to ensure that the condition does not progress.
Once the condition progresses, your doctor may advise you to undergo any of the following procedures, all of which are designed to alleviate harmful symptoms until the time of delivery, when the twins no longer need to share a placenta:
- Serial amniocentesis: A procedure that is used periodically to relieve the recipient twin of the excess accumulation of amniotic fluid. For this procedure, a needle is used to enter the mother's uterus and the recipient twin's amniotic sac, which is drained of fluid.
- Amniotic septostomy: A procedure in which a needle is inserted into the mother's abdomen, and the membrane between the two twins is punctured to allow equilibration of amniotic fluid between the two sacs, giving the smaller fetus more amniotic fluid.
- Umbilical cord ligation (tying of the umbilical cord): This surgery is performed endoscopically (through a small puncture in the mother's abdomen) when one twin is severely compromised with impending death. If one twin dies the other is at high risk for neurological damage caused by a severe drop in blood pressure. The procedure should offset the drop in blood pressure and prevent other continued symptoms in the surviving twin.
- Endoscopic laser surgery: A procedure in which a small puncture is made on the mother's abdomen and endoscope is inserted into the amniotic cavity. This allows the surgeon to look into the uterus and use a laser to interrupt abnormal connections between the twins.
What is the long-term outlook?
The outlook depends on the severity of the condition and how far it's progressed. Some studies have shown, however, that twin fetuses with advanced TTTS have a better survival rate after undergoing either amniotic septostomy or endoscopic laser surgery than those who undergo the other treatments discussed above.
Approximately 80 percent of fetuses with TTTS will die if there is no treatment at all. When one fetus dies, there is a high incidence of brain injury to the other fetus.
With umbilical cord ligation, brain injury might be prevented in the surviving twin. Some survivors may do well and be completely healthy, while others may have injuries to their hearts and kidneys. There is also a risk of preterm delivery after any of these procedures.
How we care for TTTS
Through the joint work of researchers, genetic specialists, surgeons, and other care providers, the Boston Children's Hospital Maternal Fetal Care Center is breaking ground in understanding and successfully treating a wide variety of fetal health concerns, including TTTS.