Twin-to-Twin Transfusion Syndrome

What is twin-to-twin transfusion syndrome?

Twin-to-twin transfusion syndrome (TTTS) is a rare condition in pregnancies involving identical twins. Each twin has a separate amniotic sac, the fluid-filled sac that protects a fetus in the uterus. But, the twins share a placenta, the organ that provides the oxygen- and nutrient-rich blood that a fetus needs to grow and survive.

While most identical twins in utero share blood and nutrients from the same placenta equally, twins affected by TTTS don’t. Instead, one twin shares too much blood (the donor) with the other twin (recipient). The imbalanced blood flow can create problems for both twins’ development without treatment.

Donor twin

The donor twin shares too much blood from the placenta with the recipient twin. As a result, the donor doesn’t receive enough nourishment. Also, the donor pees less. Less peeing causes the amniotic sac — which consists primarily of urine — to shrink or even disappear.

A shrinking amniotic sac is concerning because it cushions and protects a growing fetus in the uterus. Also, it’s filled with nutrients that a fetus needs to ingest to support organ development.

Recipient twin

The recipient twin receives too much blood from the donor twin. While the donor twin’s body is malnourished, the recipient twin’s body is overworked. The recipient’s body has to process too much blood, leading to an amniotic sac that’s much larger than the donor’s.

Without treatment, both twins are at risk for cardiovascular problems and even death. Twin-to-twin transfusion syndrome requires close monitoring and treatment from your provider to prevent these outcomes when possible.

Who does it affect?

Twin-to-twin transfusion syndrome affects people who are pregnant with identical twins. The twins share a placenta (monochorionic) but have separate amniotic sacs (diamniotic). The condition doesn’t affect people who are pregnant with fraternal twins.

How common is twin-to-twin transfusion syndrome?

About 6% to 15% of identical twin pregnancies involve twin-to-twin transfusion syndrome.

What causes twin-to-twin transfusion syndrome?

In typical pregnancies involving identical twins, both fetuses equally share the nutrient- and oxygen-rich blood from the placenta. The blood vessels in the placenta connect so that each twin receives the same amount of blood. As a result, both twins develop at more or less the same rate within their separate amniotic sacs.

Twin-to-twin transfusion syndrome occurs when the blood vessels in the placenta connect in a way that prohibits even blood flow between twins. It’s unclear what causes the faulty connection. Still, it results in one twin receiving too little blood and the other receiving too much blood.

What are the symptoms of twin-to-twin transfusion syndrome?

Twin-to-twin transfusion syndrome doesn’t involve traditional symptoms in the way that many conditions do. Instead, you’ll receive a diagnosis based on findings from a prenatal ultrasound.

How is twin-to-twin transfusion syndrome diagnosed?

Your healthcare provider may discover TTTS during a routine prenatal ultrasound. During your exam, your healthcare provider may notice that one of your twins has a larger amniotic sac than the other twin. A Doppler ultrasound can show irregularities in the blood flow between twins and also help with the diagnosis. Fetal echocardiography (echo) can allow your provider to assess each twin’s heartbeat, which helps with diagnosis, too.

Your provider may request a fetal MRI or contact a maternal-fetal medicine specialist to help confirm a TTTS diagnosis. A maternal-fetal specialist can do additional tests to assess each twin’s blood flow, bladder function, and amount of amniotic fluid.

Your provider will also assess your health. The increase in amniotic fluid from the recipient twin can cause your uterus to get bigger and your cervix to shorten. These changes can lead to preterm labor.

What are the stages of TTTS?

Part of your diagnosis involves assessing the severity of your condition. The Quintero staging system allows your provider to determine how much your TTTS has progressed so that they can recommend the best treatment options.

Quintero staging system

• Stage 1: The donor twin’s amniotic sac is smaller than the recipient donor’s amniotic sac. But, it’s big enough to show that the donor is getting enough blood and nutrients.
• Stage 2: The donor twin’s amniotic sac isn’t visible on the ultrasound. The lack of an amniotic sac means that the donor has stopped making urine.
• Stage 3: A substantial imbalance in the blood flow between twins negatively impacts the heart function in one or both twins.
• Stage 4: One or both twins is showing signs of heart failure.
• Stage 5: One or both twins has passed away.

How is twin-to-twin transfusion syndrome managed?

Your healthcare provider will monitor your pregnancy closely. Often, a care team will offer clinical and emotional support throughout your pregnancy. Care team members may include maternal-fetal medicine specialists, fetal interventionists, pediatric cardiologists, neonatologists, nurse specialists, perinatal social workers, other technical specialists, and surgeons.

You’ll need frequent ultrasounds and fetal echocardiograms during your pregnancy. During your second trimester, you may get an ultrasound as frequently as every two weeks. This frequency may increase during your third trimester. Follow your provider’s advice about how frequent your ultrasounds should be.

What is the treatment for twin-to-twin transfusion syndrome?

Treatment for twin-to-twin transfusion syndrome depends on how far along you are in your pregnancy and your twin-to-twin transfusion syndrome stage.

• Expectant management. Your provider will monitor your pregnancy closely with ultrasounds and echocardiograms. Expectant management is common during stage 1 TTTS.
• Amnioreduction: This procedure is similar to amniocentesis. Your provider will use a small, hollow needle to drain excess amniotic fluid from the recipient twin. Your provider may recommend amnioreduction during stage 1 TTTS or in more advanced stages of TTTS.
• Fetoscopic laser photocoagulation: This surgery uses a laser to close off the blood vessels in your placenta that are causing uneven blood flow between your twins. Afterward, your twins will receive blood directly from the placenta instead of sharing.
• Delivery. If you’re diagnosed with TTTS later in your pregnancy, your provider may recommend a c-section. Or, they may admit you to the hospital in case you go into labor before your due date. Early labor is common with twin-to-twin transfusion syndrome.

How can I prevent twin-to-twin transfusion syndrome?

There’s no way to prevent twin-to-twin transfusion syndrome. And there’s nothing that you did or didn’t do that caused it.

The outcomes for twin-to-twin transfusion syndrome depend on the amount of time your twins developed in your uterus before birth and the treatment you received. When you receive your diagnosis matters, too.

Often, your babies will need to be delivered early. Many twins in TTTS pregnancies will need to spend some time in the NICU after they’re born to give them the start they need.

What is the survival rate for twin-to-twin transfusion syndrome?

Receiving appropriate treatment makes all the difference when it comes to the outcomes associated with TTTS. About 90% of twins diagnosed in the later stages of TTTS who don’t receive treatment pass away before birth. With treatment, the odds reverse. In about 90% of pregnancies that involve treatment, at least one twin survives.

Half of TTTS pregnancies involve both twins surviving. Talk with your provider about the prognosis for your twins.

What questions should I ask my doctor?

• How will my pregnancy be different from a pregnancy involving twins without TTTS?
• Will I need to see a specialist? Who is on my care team?
• How will TTTS affect plans for delivery?
• Will I feel any changes in my body because of TTTS? If so, what should I expect?
• What lifestyle habits (eating, exercise, rest, therapy etc.) would you recommend to support my health during this time?

A note from Cleveland Clinic

Receiving a diagnosis of twin-to-twin transfusion syndrome can be scary. It’s common to experience fear and anxiety about what comes next for both you and your twins. Speak with your provider about treatment options that work best based on your unique situation. Reach out to friends and family members for support as you progress through your pregnancy. Joining support groups for families who have experienced TTTS can provide additional support that can help you along your journey.