Twin-to-Twin Transfusion Syndrome

What is twin-to-twin transfusion syndrome?

Twin-to-twin transfusion syndrome (TTTS) is a rare, serious condition in pregnancies involving identical twins who share one placenta (also called monochorionic twins). While most identical twins share blood and nutrients from the same placenta equally, twins affected by TTTS don’t. Instead, one twin (the donor twin) receives less blood supply than the other twin (the recipient twin). This means the donor twin has less blood volume, but the recipient twin has more blood volume. This blood flow imbalance can cause TTTS.

Twin-to-twin transfusion syndrome requires close monitoring from a maternal-fetal medicine (MFM) specialist. Early detection, monitoring and treatment are crucial for improving the outcome for both twins.

Donor twin

The donor twin receives less blood flow from the placenta compared to the recipient twin. As a result, the donor twin has less blood volume. This can lead to slower growth and decreased amniotic fluid volume. The donor twin urinates less. Since amniotic fluid is made up mostly of urine (pee), the amniotic sac can shrink or even disappear. When the amniotic fluid is low, the membrane or sac that the donor fetus is in can collapse around it. A shrinking amniotic sac is concerning because it can affect the movement of the fetus and can compress the umbilical cord.

Recipient twin

The recipient twin receives too much blood volume from the placenta. The excess blood volume can put a strain on the recipient twin’s heart, leading to heart failure. While the donor twin’s body can be undernourished, the recipient twin’s body is overworked. The recipient fetus has to process too much blood volume and makes more urine than is typical, leading to an amniotic sac that’s much larger.

Who does TTTS affect?

Twin-to-twin transfusion syndrome affects people who are pregnant with identical twins that share one placenta (monochorionic twins). In most cases of TTTS, the twins have two separate amniotic sacs (diamniotic). These types of twins are called monochorionic diamniotic.

TTS can also happen when twins share both a placenta (monochorionic) and an amniotic sac (monoamniotic), but these types of twins are less common.

How late in pregnancy can twin-to-twin transfusion syndrome develop?

TTTS typically develops as early as 16 weeks of pregnancy, but it can develop at any time during pregnancy.

How common is twin-to-twin transfusion syndrome?

Approximately 15% of identical twin (monochorionic) pregnancies will develop twin-to-twin transfusion syndrome.

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

Twin-to-twin transfusion syndrome doesn’t cause symptoms most of the time. For those that do experience symptoms, they could include:

• Rapid uterine growth or measuring large.
• Abdominal pain or tightness.
• Sudden weight gain.

What causes twin-to-twin transfusion syndrome?

In typical pregnancies involving twins with one placenta (monochorionic), both fetuses equally share the same blood volume from the placenta. With TTTS, the blood vessels connect in the placenta in a way that allows blood volume to be distributed unequally, with the recipient twin getting more and the donor twin getting less.

How the placenta develops is beyond your control. TTTS happens by chance and it’s not because of something you did or didn’t do. There’s no way to prevent twin-to-twin transfusion syndrome.

What puts people at risk for TTTS?

There isn’t a genetic or hereditary component to TTTS. It’s random but can only happen in identical twin pregnancies where both fetuses share a placenta (monochorionic).

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

When left untreated or in severe cases that occur early in pregnancy, twin-to-twin transfusion is associated with high morbidity and mortality. It’s essential that you receive treatment or close monitoring from an MFM specialist or fetal care center. Even with early treatment, theres a risk of pregnancy loss.

Other complications of TTTS, in general, are:

• Complications of premature birth that could include respiratory issues, neurological conditions and others.
• Recipient twin may have heart failure or other cardiac conditions due to excess fluid.
• Donor twin may have a growth delay or kidney injury.

How is twin-to-twin transfusion syndrome diagnosed?

Your pregnancy care provider will diagnose twin-to-twin transfusion syndrome with an ultrasound. The first thing your provider will see on an ultrasound is a twin pregnancy with fetuses sharing one placenta.

If your pregnancy care provider suspects TTTS, they’ll refer you to a specialist in maternal-fetal medicine (MFM) for further testing. From there, the MFM will notice one or more of the following on ultrasound:

• A difference in the size of the fetuses.
• One twin has too much amniotic fluid, while the other has too little.
• Irregularities in blood flow between the twins (on a Doppler ultrasound).

In some cases, a fetal MRI (magnetic resonance imaging) and fetal echocardiography (echo) may be necessary.

Your pregnancy care team will monitor you very closely for the rest of your pregnancy. You’ll need frequent ultrasounds to assess the twins’ health.

Your provider will also assess your health. Sometimes, the increased amniotic fluid from the recipient can cause your uterus to get bigger and your cervix to weaken. These changes can lead to preterm labor and early delivery.

What are the stages of TTTS?

Part of the ultrasound evaluation involves assessing the stage of TTTS or how severe it is. This allows your physician to follow the progression so that they can recommend the best treatment options.

There are five stages of TTTS:

• Stage 1: The donor twin has little to no amniotic fluid as compared to the recipient twin who likely has too much.
• Stage 2: The donor twin’s bladder isn’t visible on ultrasound. It typically means that the donor twin has stopped making urine.
• Stage 3: A substantial imbalance in the blood flow between twins, which can sometimes impact the heart function in one twin.
• Stage 4: One or both twins are showing signs of skin or body swelling.
• Stage 5: One or both twins have passed away.

Stage 1 TTTS may only need monitoring or close observation. Progression can happen very quickly (if it does happen). Once TTTS progresses to stage 2, fetal surgery is usually offered if you’re less than 26 weeks.

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 what stage of TTTS you have:

• Observation and monitoring: Your provider will monitor your pregnancy closely with ultrasound. Observation is an option if you have stage 1 TTS or have reasons why surgery or other interventions can’t happen.
• Septostomy: This is a procedure that involves making a small hole in the dividing membrane between the twin’s amniotic sacs. This can equalize the pressure in each amniotic sac. It’s relatively low risk but doesn’t treat the underlying cause of TTTS.
• Amnioreduction: Your provider will use a small, hollow needle to drain excess amniotic fluid from the recipient twin’s sac. Your provider may recommend amnioreduction during stage 1 TTTS or in more advanced stages of TTTS occurring later in pregnancy. Because this doesn’t treat the underlying cause of TTTS, if the amniotic fluid increases again, you may need to have more than one amnioreduction.
• Fetoscopic laser ablation: This surgery uses a tiny camera in the uterus (fetoscope) and a laser that closes off the blood vessels on the placenta surface that are causing uneven blood flow between the twins. The goal of the surgery is to shift blood flow from one fetus toward the other. This allows each twin to have its own blood volume instead of sharing. This surgery is an option for stage 2 TTTS or higher and between 16 to 26 weeks gestation.
• Umbilical cord occlusion: Your provider may recommend this procedure as a last resort when it’s not possible to save both twins or one fetus has a life-threatening condition. The surgery blocks blood flow to one twin, which gives the other twin the best chance at survival.
• Delivery: Your provider may recommend delivery if you’re at a viable gestational age (a time when a baby can survive outside of the body).

Your healthcare team can help you determine which treatment is the best option. They’ll answer any questions you have and discuss the risks, benefits and alternatives to each of the procedures with you.

How is twin-to-twin transfusion syndrome managed?

Your healthcare provider will monitor your pregnancy closely with the MFM specialist. You’ll need frequent ultrasounds (often weekly or semiweekly) and, possibly, a fetal echocardiogram during your pregnancy. Your care team will offer both medical and emotional support throughout your pregnancy.

What can I expect if I have this condition?

The outcomes for twin-to-twin transfusion syndrome depend on the gestational age you receive a diagnosis and how serious it is (stage). Advances in medicine make it possible, with close monitoring and quick treatment, for both twins to have a better chance of surviving. You should discuss expectations and possible outcomes with your provider so that you understand what TTTS means for your pregnancy and your twins. Most surviving twins will need to spend some time in the NICU after they’re born to give them the start they need.

TTTS can be a highly emotional and stressful experience. Make sure you take care of yourself and lean on your healthcare team, partner(s) and friends for support.

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

The survival rate depends on how severe the TTTS is, when you receive a diagnosis and if you get treatment. Receiving appropriate treatment makes all the difference when it comes to the survival rates with TTTS:

• About 90% of twins diagnosed with an advanced stage of TTTS very early in pregnancy are at risk of passing away before birth.
• In about 85% to 90% of TTTS pregnancies that receive treatment, at least one twin survives.
• In about 50% to 65% of TTTS pregnancies that receive treatment, both twins survive.

Talk with your care team about the prognosis (outlook) for your twins, as there are so many factors that play a role in survival.

What questions should I ask my healthcare team?

Some questions you may want to ask include:

• How will my pregnancy be different from a pregnancy involving twins without TTTS?
• Will I need to see a specialist? Who’s on my care team?
• How often will I need imaging tests or other tests?
• 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 treatment do you recommend based on my situation and why?
• What lifestyle habits (eating, exercise, rest, therapy and more) would you recommend to support my health?

What is a daisy baby?

A daisy baby is another name for babies with TTTS. The Twin-to-Twin Transfusion Syndrome Foundation coined the term after its founder planted daisy seeds with her surviving twin son in their backyard. The daisy field is a symbol of hope that all babies affected by TTTS will survive.

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’ve experienced TTTS can provide additional support to help you along your journey.