Twin-to-Twin Transfusion Syndrome

Twin-to-twin transfusion syndrome (TTTS) is a disease of the placenta that occurs in identical twins or other multiples with a single placenta.

In TTTS, shared blood vessels support the growing babies unequally. Unequal exchange of blood results in size and health differences between the babies.

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On this page:

• What Is Twin-to-Twin Transfusion Syndrome?  
• What Are the Symptoms of Twin-to-Twin Transfusion Syndrome?  
• How Do You Diagnose Twin-to-Twin Transfusion Syndrome?
• How Do You Treat Twin-to-Twin Transfusion Syndrome?  

What Is Twin-to-Twin Transfusion Syndrome?  

Doctors define twin-to-twin transfusion syndrome (TTTS) as a rare disease of the placenta — the organ that joins mothers and babies and provides nourishment to growing fetuses. TTTS occurs when monozygotic (identical) twins or multiples supported by a single placenta — known as a monochorionic placenta — receive unequal amounts of blood from shared blood vessels.

Unequal blood flow in TTTS affects the amount of nutrients and oxygen the babies receive, resulting in a diminished ability to grow or survive.

Other names for twin-to-twin transfusion syndrome include: 

• TTTS.
• Twin-twin transfusion syndrome.
• Twin-to-twin transfusion.

TTTS can occur at any time during pregnancy, including at delivery.

How common is TTTS? 

Approximately 15% of all identical twin or multiples pregnancies develop TTTS. TTTS complicates 8% to 10% of monochorionic diamniotic (MCDA) and 6% of monochorionic monoamniotic (MCMA) twin gestations.

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

TTTS is a serious condition that's either chronic or acute.

Chronic twin-to-twin transfusion syndrome

• Appear early in pregnancy (between 12 to 26 weeks’ gestation).
• Are the most serious because the babies are immature and cannot be delivered.

Without treatment, chronic TTTS babies face handicaps, birth defects, or death.

Acute twin-to-twin transfusion syndrome

• Appear suddenly in pregnancy when there are major differences in blood pressures between twins.
• May occur in labor at-term or during the last trimester of pregnancy.

Acute TTTS babies have a better chance of survival based on gestational age and may have a greater chance of surviving with handicaps.

What causes twin-to-twin transfusion syndrome?  

Monozygotic (identical) twins start as a single zygote in the womb. The type of placenta in identical twins is determined by when zygotic splitting occurs. When splitting occurs between days 3 to 13 of gestation, the babies share a single placenta.

Most babies sharing a placenta also share blood vessels that connect the blood circulations of both babies. In TTTS, the “donor” twin donates more blood to the other twin than it receives in return from the “recipient” twin.

What are twin-to-twin transfusion syndrome risk factors and complications?  

Twin-to-twin transfusion syndrome risk factors

The type of twin gestation is a risk factor in TTTS:

• Monochorionic diamniotic (MCDA) twin gestations — When twin babies share one placenta but have individual amniotic sacs. TTTS occurs in approximately 8% to 10% of MCDA twin gestations.
• Monochorionic monoamniotic (MCMA) twin gestations — When twin babies share one placenta and one amniotic sac. TTTS occurs in approximately 6% of MCMA twin gestations.

Complications of twin-to-twin transfusion syndrome

TTTS can cause:

• Digestive defects in one or both babies.
• Heart disease or defects in one or both babies.
• Lung defects in one or both babies.
• Neurological abnormalities in one or both babies.
• Premature labor or delivery.
• Death of one or both babies.

Left undiagnosed or untreated, this condition can cause further complications or lead to other health problems, including fetal death.

How can I reduce my risks of twin-to-twin transfusion syndrome?  

Close monitoring by your ob-gyn can help reduce the risks of TTTS. In twin pregnancies where babies share one placenta, biweekly ultrasound screening for TTTS is recommended starting at the second trimester until the end of pregnancy.

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What Are the Signs and Symptoms of Twin-to-Twin Transfusion Syndrome? 

Approximately half of women diagnosed with twin-to-twin transfusion syndrome experience symptoms before diagnosis.

Symptoms of TTTS include:

• Abdominal pain or tightness.
• Contractions.
• Decreased fetal movement.
• Nausea.
• Sensation of rapid growth of the womb.
• Sudden increase in body weight.
• Swelling in the hands and legs in early pregnancy. 
• Uterus measurements that are large for gestational dates.
• Vaginal pressure.

When should I see a doctor about my twin-to-twin transfusion syndrome symptoms? 

Visit your doctor at the onset of TTTS symptoms. If you don't experience symptoms but have questions or concerns about TTTS, ask your doctor about monitoring throughout your pregnancy.

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How Do You Diagnose Twin- to-Twin Transfusion Syndrome?  

Doctors use ultrasound to diagnose and monitor TTTS.

There are five diagnostic stages of TTTS: 

• Stage 1 — There's a noticeable size difference between the amniotic sacs of each baby. The donor baby’s bladder is visible in an ultrasound.
• Stage 2 — The donor baby’s bladder isn't visible in an ultrasound.
• Stage 3 — Doppler abnormalities and abnormal blood flow are detectable by ultrasound. Size difference between babies may be detectable.
• Stage 4 — One or both twins may show signs of heart failure or large amounts of fluid buildup in tissues and organs.
• Stage 5 — Demise of one or both twins.

Twin-to-Twin transfusion syndrome survival rate

With treatment, the single twin survival rate is approximately 88%, while the survival rate for both twins is about 65%.

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How Do You Treat Twin-to-Twin Transfusion Syndrome?  

We treat twin-to-twin transfusion syndrome with fetoscopic laser surgery.

This treatment:

• Is minimally invasive, using a laser to disconnect babies’ shared blood vessels endoscopically.
• Takes about one hour to complete.
• Is performed by maternal fetal medicine specialists.

What happens during fetoscopic laser surgery? 

Your maternal fetal medicine specialist will:

• Make a small incision where the endoscope is inserted.
• Endoscopically insert a laser into the womb
• Burn and seal the interconnecting blood vessels, restoring normal blood flow.

The procedure doesn't hurt. Your doctor will administer local anesthesia and intravenous (IV) sedatives during surgery. Most people return to regular daily activities within three weeks.

Risks and side effects fetoscopic laser surgery include:

• Psychological symptoms.  
• Premature rupture of membrane (your water breaking).
• Preterm labor.
• Pulmonary edema.
• Uterine bleeding.

How effective is fetoscopic laser surgery?

Fetoscopic laser surgery (FSL) is safe for the mother with no impact on fertility, future pregnancies, or overall gynecologic health.

Studies show that FSL results in high survival rates and low rates of neurological complications. This procedure is used at fetal treatment centers around the world for TTTS to improve the survival rate and neurological outcomes.

By UPMC Editorial Staff. Last reviewed on 2024-09-05.