Definition

Twin-to-twin transfusion syndrome (TTTS) is a condition that occurs in twin pregnancies, where blood flows unevenly between twin fetuses sharing a single placenta in identical twins. TTTS occurs in about 10-15% of monochorionic diamniotic twins (only one placenta and two amniotic sacs in the pregnancy). This condition does not occur in non-identical twins.

If you want to read more about twin pregnancies, you can read here: Twin Pregnancy - Definition, Causes, Symptoms, and Treatment.

If you want to read more about twin pregnancies, you can read them here: Twin Pregnancy - Understanding, Causes, Symptoms, And Treatment.

Causes

Each twin has its own amniotic sac, which contains amniotic fluid that protects the fetus in the womb. Most identical twins share the same placenta. When more than one baby shares one placenta, they also share blood vessels. Normally, blood flow for both babies will be balanced so they can grow and develop normally.

However, in TTTS, blood flow becomes imbalanced between identical twins, causing one fetus to donate blood to the other. The fetus donating blood is referred to as the donor twin, while the fetus receiving blood is referred to as the recipient twin. This causes the recipient twin to receive more blood, while the donor twin receives less.

As a result, the distribution of blood and nutrients from one placenta to the babies becomes uneven. One twin receives more blood and nutrients compared to the other. This can become a problem for the twins' development if they do not receive treatment.

Risk Factor

Being pregnant with identical twins puts the mother at risk of experiencing TTTS. However, TTTS does not always occur in identical twin pregnancies. A history of TTTS in a previous pregnancy does not increase your risk of experiencing TTTS in a subsequent pregnancy.

Symptoms

Fetal symptoms

In TTTS, increased blood volume causes the recipient twin to produce more urine than usual, which can lead to:

• Enlargement of the fetal bladder
• Excessive amniotic fluid (polyhydramnios)
• Hydrops fetalis (a form of heart failure in the fetus)

The donor twin, receiving too little blood, will produce less urine than normal, leading to decreased or absent amniotic fluid around it (oligohydramnios) and a small or absent bladder.

Maternal symptoms

Mothers carrying fetuses with TTTS may experience abdominal discomfort due to one fetus having excess amniotic fluid. TTTS is divided into several stages:

• Stage 1: In the early stage, uneven blood flow between the twins sharing one placenta causes the recipient twin to have excess amniotic fluid and the donor twin to have little or no amniotic fluid.
• Stage 2: In stage 2, the donor twin’s bladder does not fill or release urine, as minimal blood is allocated from the kidneys to the brain, heart, and adrenal glands (glands located above the kidneys). The body sends blood to vital organs as a defense mechanism to maintain the function of important organs. The kidneys and bladder continue to function but slower than normal, so normal bladder filling and emptying are not seen.
• Stage 3: In stage 3, abnormal blood flow patterns indicate heart function disorders in one or both fetuses.
• Stage 4: In stage 4, excessive fluid accumulation occurs, which poses a risk to the mother and her fetuses. Heart failure may be indicated in the recipient twin. The recipient twin’s heart works hard to process the excess blood received from the donor twin.
• Stage 5: In the final stage, the death of one or both fetuses may occur inside the mother's womb.

Diagnosis

The most crucial step in evaluating twin pregnancies with TTTS is determining whether the fetuses share one placenta. Early pregnancy ultrasound examinations (during the first trimester) can best show this condition.

In TTTS, fetuses may be found with different sizes and varying volumes of amniotic fluid surrounding each fetus. More detailed ultrasound examinations can rule out other structural abnormalities.

Examinations that can be performed include:

• High-Resolution Ultrasound: This examination is used to ensure no abnormal structures in the fetuses. It can also confirm the location of the placental attachment and the attachment of the umbilical cord to the placenta, assess the volume of amniotic fluid in each amniotic sac, and evaluate blood flow patterns in specific blood vessels for each fetus.
• Fetal Echocardiography (ECG): EKG focuses on the fetal heart to detect any related heart conditions. TTTS can cause serious heart fatigue in the recipient fetus, leading to heart enlargement and heart function disorders. All fetuses evaluated for TTTS should undergo fetal EKG.
• Genetic Amniocentesis: This procedure involves taking a small amount of amniotic fluid from the amniotic sac surrounding the fetus, and this sample is then examined. In some cases, genetic testing may be needed if structural abnormalities accompanying TTTS are found in radiology examinations.

Management

Mothers require close monitoring and care to prevent unwanted events. TTTS treatment and therapy include:

• Close monitoring: In situations where surgery is not yet indicated (stage 1 without other risk factors), close monitoring with regular ultrasound examinations will be conducted to evaluate the condition of both fetuses and look for signs of disease progression.
• Selective Fetoscopic Laser Ablation: This minimally invasive procedure (which uses only small incisions with faster healing time) is performed on the placenta to cut off blood vessel connections. This procedure, also known as selective laser photocoagulation, stops the blood sharing from the donor twin to the recipient twin.
  It is hoped that the disease will not worsen and can be resolved. This treatment is usually the choice for TTTS, depending on the gestational age, placental location, and TTTS stage.
• Amnioreduction: Removing excess amniotic fluid from the recipient twin can help reduce pain or discomfort felt by the mother due to fluid buildup. This is a temporary therapy option and may need to be repeated.
• Selective Umbilical Cord Occlusion: This minimally invasive procedure is also performed to stop blood flow to one twin. This procedure is done in advanced TTTS stages where the twin cannot survive. This procedure can protect the surviving twin from neurological disorders and/or death.

Complications

The prognosis for babies with TTTS depends on how quickly the condition is addressed and the baby's gestational age at birth. The sooner the baby receives therapy and the longer the baby stays in the womb before birth, the fewer the complications. TTTS can significantly impact the fetal cardiovascular system. If left untreated, this condition can potentially cause membrane rupture and premature labor.

After babies with TTTS are born, complications from premature birth or the effects of the disease while in the womb can occur. Babies with low birth weight have a higher risk of neurological disorders such as mental retardation, cerebral palsy, vision problems, and hearing problems. Babies born between 24 and 32 weeks are at high risk for disabilities.

If you want to read more about cerebral palsy, you can read it here: Cerebral Palsy - Definition, Cause, Symptom, And Treatment.

Prevention

TTTS is an unpredictable condition that cannot be prevented. However, pregnant mothers can have regular prenatal check-ups to quickly detect this condition and receive immediate treatment.

When to See a Doctor?

Usually, TTTS is discovered during routine pregnancy check-ups by a doctor. However, if you experience symptoms or discomfort during pregnancy, it is advisable to see a doctor.

Looking for more information about other diseases? Click here!