Twin pregnancy is always a journey filled with joy and anticipation, but in some rare cases it can turn into a serious medical challenge that requires very close monitoring. One of the most important of these conditions is Twin-to-Twin Transfusion Syndrome (TTTS).This syndrome occurs when identical twins share a single placenta, leading to an imbalance in blood flow between them. As a result, one twin becomes the “donor,” losing blood and fluids, while the other becomes the “recipient,” receiving an excessive amount. This imbalance can affect growth and disrupt normal body functions in both fetuses.Although this condition may sound alarming, major advances in fetal medicine—especially early diagnosis techniques and intrauterine laser treatment—have significantly improved survival rates and reduced complications.In this Delly Medical article, we take you on a simple and comprehensive journey to understand TTTS: its causes, symptoms, methods of diagnosis, the latest treatment options, and how it can be managed to protect both twins as much as possible.

1) What is Twin-to-Twin Transfusion Syndrome (TTTS)?
It is a condition that occurs in identical twin pregnancies that share a single placenta. In this situation, there is an abnormal connection of blood vessels within the placenta, which leads to an uneven distribution of blood between the two fetuses. As a result, each twin receives an unbalanced amount of blood supply.

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⚠️ 2) Is TTTS a dangerous condition?
Yes, TTTS can be serious if it is not diagnosed early and closely monitored. It may negatively affect:

• Fetal growth of one or both twins
• Heart function of one or both fetuses
• The level of amniotic fluid around each fetus

In severe cases, it can even threaten the life of one or both twins.

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3) Can TTTS cause long-term disabilities after birth?
In some cases, TTTS may lead to long-term complications, especially if the condition is severe or if preterm birth occurs, such as:

• Delayed motor or cognitive development
• Neurological development issues
• Complications related to premature birth

However, early diagnosis and proper treatment—such as fetal laser surgery—significantly improve the chances of delivering healthy babies or minimizing complications.

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Causes of Twin-to-Twin Transfusion Syndrome (TTTS)

TTTS occurs in identical twin pregnancies where both fetuses share a single placenta (monochorionic pregnancy). This shared placenta contains blood vessel connections between the two fetuses.

Main cause
TTTS is not a blood disease. It is a disorder of blood flow distribution within the placenta due to abnormal vascular connections between the twins.

How does it happen?
Inside the shared placenta, blood vessels connect the circulations of both fetuses, and under normal conditions, blood exchange is balanced.

However, in TTTS this balance is disrupted, leading to:

• Excess blood flow from one twin to the other
• One twin becoming the “donor”
• The other twin becoming the “recipient” 

⚠️ Factors that lead to or increase the risk of Twin-to-Twin Transfusion Syndrome (TTTS)

1) Single shared placenta
This is the most important factor.
TTTS only occurs in monochorionic twin pregnancies, where both fetuses share one placenta.

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2) Abnormal placental vascular connections
There are uneven and abnormal connections between arteries and veins inside the placenta.
This causes blood to flow in one direction in an unbalanced way between the twins.

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❤️ 3) Difference in blood pressure between both fetuses
Variations in vascular pressure allow continuous blood transfer from one twin to the other.

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4) Abnormal blood vessel formation in early pregnancy
This happens during the early weeks of placental development and leads to an irregular vascular network inside the placenta.

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Final outcome of the imbalance

• Donor twin: suffers from reduced blood flow and fluid loss, leading to dehydration and poor growth
• Recipient twin: receives excess blood, which may cause heart strain and increased amniotic fluid

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Stages (Severity Levels) of TTTS – Quintero Staging

TTTS is not divided into types, but into stages based on severity, known as the Quintero Staging System, which is used to guide treatment decisions.

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Stage I – Mild

• Mild difference in amniotic fluid levels
• Donor twin: reduced fluid around the fetus
• Recipient twin: increased fluid
• Donor’s bladder is still visible on ultrasound
• Usually managed with close monitoring

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Stage II – Moderate

• More obvious imbalance in amniotic fluid
• Donor’s bladder is not visible on ultrasound
• Blood flow parameters remain relatively stable
• Requires close follow-up and may need intervention

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Stage III – Severe

• Serious abnormalities in blood flow (Doppler studies)
• Possible effects on brain, umbilical cord, or heart circulation
• Signs of cardiac strain in the recipient twin
• Often requires intrauterine laser treatment

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Stage IV – Heart failure stage

• Recipient twin develops hydrops fetalis (fluid accumulation in the body)
• Indicates heart failure due to severe circulatory overload
• Critical condition requiring urgent intervention

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Stage V – Fetal death

• Death of one or both twins inside the womb
• Usually due to severe imbalance in blood circulation

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Symptoms of TTTS

TTTS is usually detected during ultrasound scans, but some signs may be noticed in the mother or during medical evaluation.

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1) Maternal symptoms

In some cases, the mother may notice:

• Rapid increase in abdominal size
• Feeling of heaviness or tightness in the abdomen
• Sudden weight gain over a short period
• Shortness of breath due to excess amniotic fluid
• Early uterine contractions or signs of preterm labor

These symptoms are often linked to increased amniotic fluid around the recipient twin.

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2) Ultrasound findings (most important for diagnosis)

Donor twin:

• Severe reduction in amniotic fluid
• Small or non-visible bladder
• Growth restriction compared to the co-twin
• Compressed appearance inside the uterus

Recipient twin:

• Excess amniotic fluid
• Enlarged or consistently full bladder
• Larger size compared to the donor twin
• Possible signs of cardiac stress

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3) Advanced-stage symptoms

In severe cases:

• Reduced fetal movements in one twin
• Abnormal heart rhythm
• Fluid accumulation in the recipient twin (hydrops fetalis)
• High risk of very preterm delivery

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Diagnosis of TTTS

TTTS is primarily diagnosed through ultrasound imaging during pregnancy, especially in monochorionic twin pregnancies.

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1) Determining chorionicity

The first and most important step is confirming that the twins are:

• Monochorionic (sharing one placenta)
  This is essential for TTTS to occur.

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2) Ultrasound examination

The doctor looks for key signs:

Donor twin:

• Severe oligohydramnios (very low amniotic fluid)
• Small or absent bladder
• Growth delay compared to the co-twin

Recipient twin:

• Excess amniotic fluid (polyhydramnios)
• Enlarged bladder
• Larger size than the donor twin
• Possible signs of cardiac strain

Third: Key Diagnostic Criteria
Diagnosis also relies on two main criteria:

✔️ 1) Amniotic fluid imbalance

• Severe reduction of amniotic fluid in one sac
• Marked increase in the other sac

✔️ 2) Bladder assessment

• Non-visualization of the donor twin’s bladder on ultrasound

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Fourth: Classification after diagnosis
Once TTTS is confirmed, its severity is determined using the Quintero Staging System, which helps guide the appropriate treatment plan.

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Fifth: Additional tests (in advanced cases)
In more severe situations, advanced investigations may be used, such as:

• Doppler studies of the umbilical cord arteries
• Assessment of blood flow to the brain and heart
• Detailed fetal cardiac evaluation, especially for the recipient twin

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Complications of Twin-to-Twin Transfusion Syndrome (TTTS)

TTTS is one of the most serious complications of monochorionic twin pregnancy because it causes a severe imbalance in blood sharing between fetuses, leading to significant risks for both twins and the pregnancy itself.

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⚠️ 1) Complications in the Donor Twin

The twin losing blood is deprived of oxygen and nutrients, which may lead to:

• Severe oligohydramnios (very low amniotic fluid)
• Significant growth restriction
• Smaller fetal size compared to the co-twin
• Reduced oxygen and nutrient supply
• Decreased fetal movements
• In severe cases: organ failure or intrauterine death

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⚠️ 2) Complications in the Recipient Twin

The twin receiving excess blood may develop serious complications, including:

• Severe polyhydramnios (excess amniotic fluid)
• Cardiac overload due to increased blood volume
• Cardiac enlargement or heart failure
• Breathing difficulties after premature birth
• Fluid accumulation in the body (hydrops fetalis)
• Increased risk of intrauterine death in severe cases

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3) Complications affecting the pregnancy

TTTS also impacts the pregnancy as a whole, such as:

• Extreme prematurity
• Premature rupture of membranes
• Increased risk of losing one or both twins
• Need for urgent interventions such as fetal laser therapy

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4) Long-term complications after birth

Even after delivery, especially in severe or preterm cases, complications may include:

• Delayed physical growth
• Motor or cognitive developmental delay
• Neurological complications in some cases
• Heart problems in the recipient twin
• Prematurity-related complications such as lung immaturity

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Short-term and Long-term Complications of TTTS

⚠️ First: Short-term complications (during pregnancy and delivery)

This is the most critical phase, as deterioration can happen rapidly.

1) Donor twin

• Severe oligohydramnios (dry environment around the fetus)
• Reduced fetal movements
• Growth restriction
• Poor oxygen and nutrient supply
• Reduced blood flow to vital organs
• Increased risk of intrauterine death
• Possible placental complications in severe cases

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2) Recipient twin

• Severe polyhydramnios
• Overdistended uterus increasing risk of preterm labor
• Severe cardiac strain
• Heart enlargement or fetal heart failure
• Hydrops fetalis (generalized fluid accumulation)
• Circulatory instability
• Increased risk of intrauterine death

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3) Pregnancy complications

• Very preterm birth
• Premature rupture of membranes
• Strong preterm contractions
• Need for urgent intervention (laser therapy or early delivery)
• Possible loss of one or both twins in severe cases

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⚠️ Second: Long-term complications (after birth)

Even if survival is achieved, long-term effects may appear, especially in premature or severe cases:

1) Growth issues

• Delayed weight and height gain
• Slower growth compared to healthy children

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2) Neurological complications

• Delayed motor development (sitting, walking)
• Learning difficulties in some cases
• Cerebral palsy in severe cases
• Cognitive or intellectual developmental delay

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❤️ 3) Heart and circulatory problems

• Cardiac dysfunction, especially in the recipient twin
• Future blood pressure issues
• Reduced exercise tolerance

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4) Respiratory problems

• Underdeveloped lungs due to prematurity
• Need for NICU care or respiratory support after birth
• Higher risk of respiratory infections

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5) Other complications (less common)

• Vision problems
• Retinopathy of prematurity
• Hearing difficulties in some cases

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Medical treatment of TTTS using medications

It is important to understand that TTTS is caused by abnormal blood vessel connections in the placenta, so it cannot be directly treated with medications.

There is no drug that can stop blood transfer between twins or correct the abnormal placental vessels.
Therefore, medications are only supportive and not curative, and definitive treatment usually requires procedures such as intrauterine laser therapy.

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❌ Is there a direct drug treatment for TTTS?

• No medication can stop the blood imbalance between twins
• No drug can fix the placental vascular abnormality
• Therefore, drug therapy alone cannot cure TTTS

Medications are only used as supportive care alongside surgical or procedural treatment.

Second: Supportive Medications Used in TTTS

1) Tocolytic drugs (to reduce uterine contractions)

These medications are used to delay preterm labor and reduce uterine contractions:

Examples:

• Nifedipine
• Atosiban
• Terbutaline

Purpose:

• Reduce uterine contractions
• Delay delivery as long as possible
• Allow time for fetal laser treatment or further fetal development

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2) Corticosteroids for fetal lung maturity

Examples:

• Betamethasone
• Dexamethasone

Purpose:

• Accelerate fetal lung maturation
• Reduce breathing problems after premature birth
• Decrease the need for incubator or respiratory support

These are usually given when preterm delivery is expected within a few days.

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❤️ 3) Maternal supportive medications

• Intravenous fluids when needed to maintain hydration
• Antihypertensive drugs if blood pressure is high
• Iron and vitamin supplements to support pregnancy

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4) Drugs to improve circulation (experimental)

• Some medications may be used to improve blood flow
• However, their effectiveness is limited
• They are not a primary or proven treatment for TTTS

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Third: Medications that do NOT treat TTTS

• No antibiotics can treat TTTS
• No drug can balance blood flow between the twins
• No hormonal therapy can repair placental abnormalities

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⚠️ Fourth: The real role of medications in TTTS

Medications do not treat the cause, but they help to:

• Stabilize the mother’s condition
• Delay preterm labor
• Reduce complications of premature birth
• Prepare the fetuses for life outside the womb
• Support definitive treatment such as fetal laser therapy

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Treatment of Twin-to-Twin Transfusion Syndrome (TTTS)

Surgical interventions + prevention

Treatment of TTTS aims to restore balance in blood circulation between the twins or reduce complications caused by this imbalance. The choice of treatment depends on severity and gestational age. The most effective treatment is intrauterine fetal surgery.

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First: Expectant management (mild cases)

1) Close monitoring

Used in early or mild cases:

• Ultrasound every 1–2 weeks
• Monitoring amniotic fluid levels in both twins
• Continuous assessment of fetal growth

Goal: Early detection of progression and timely intervention

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Second: Main surgical treatment

2) Laser fetal surgery (Laser photocoagulation)

This is the gold standard treatment for TTTS.

Procedure:

• A small fetoscope is inserted into the uterus
• Abnormal blood vessel connections in the placenta are identified
• Laser is used to seal these abnormal vascular connections

Goal:

• Stop unbalanced blood transfer between twins
• Partially separate fetal circulations
• Reduce strain on the recipient twin’s heart

Advantages:

• Highest success rate among treatments
• Significantly reduces fetal death rates
• Improves survival of one or both twins

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Third: Amnioreduction (fluid drainage)

3) Amniotic fluid reduction

• Excess fluid is removed from around the recipient twin using a fine needle

Goal:

• Reduce uterine pressure
• Relieve maternal symptoms (e.g., shortness of breath)
• Temporarily reduce risk of preterm labor

⚠️ Note:

• Does NOT treat the underlying cause
• Considered a temporary supportive procedure

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Fourth: Cord occlusion (severe cases)

4) Selective umbilical cord occlusion

Used in very specific situations, such as:

• When one twin is non-viable
• To protect the healthier twin from complications

Methods:

• Laser
• Radiofrequency ablation (RFA)

Goal: Preserve the survival of the stronger twin

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Fifth: Radiofrequency ablation (RFA)

• A needle is inserted into the umbilical cord
• Heat is used to stop blood flow to one fetus

Used only in very severe or non-treatable cases

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Sixth: Planned preterm delivery

• Used only when pregnancy continuation becomes dangerous
• Requires neonatal intensive care preparation

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Prevention of TTTS

1) Early pregnancy assessment

• Ultrasound at 6–8 weeks
• Determine chorionicity (one placenta or two)
• Monochorionic twins are considered high risk

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2) Regular follow-up

• Ultrasound every 1–2 weeks in monochorionic twins
• Monitor amniotic fluid levels
• Assess fetal bladders and growth
• Use Doppler studies for blood flow

Goal: Early detection before progression

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3) Specialized care

• Follow-up in fetal medicine centers
• Use of advanced ultrasound technology

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4) Early intervention

Warning signs include:

• Clear difference in amniotic fluid levels
• Growth discordance between twins
• Absent bladder in one fetus

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5) General maternal advice

• Strict adherence to follow-up appointments
• Avoid excessive physical stress
• Monitor fetal movements
• Seek medical attention immediately if symptoms appear
• Maintain proper nutrition

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Long-term prognosis of TTTS

Prognosis depends on:

• Early diagnosis
• Severity of TTTS
• Timing of treatment (especially laser therapy)
• Presence of complications
• Quality of neonatal care

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First: After successful early treatment (especially laser therapy)

Growth

• Most children grow normally or near normally
• Mild early growth delay may improve over time

Neurological development

• Usually normal development
• Mild cases may show slight delays in speech or motor skills

Heart and breathing

• No permanent heart damage in most cases
• Respiratory function usually normal with proper care

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Second: Moderate or late-treated cases

Possible neurological effects

• Mild to moderate developmental delay
• Learning difficulties
• Rare cases: cerebral palsy

Growth

• Low birth weight
• Delayed catch-up growth

Respiratory issues

• Due to prematurity
• Higher risk of NICU admission
• Increased risk of infections

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Third: Severe untreated or late-treated cases

• High risk of fetal loss of one or both twins
• If born alive, possible outcomes include:
  • Permanent neurological disability
  • Severe developmental delay
  • Long-term heart or respiratory problems

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Fourth: Factors affecting long-term outcomes

• Stage of TTTS at diagnosis
• Speed of treatment initiation
• Gestational age at delivery
• Presence of hydrops fetalis
• Quality of neonatal intensive care after birth