Twin to twin transfusion syndrome

Other Names: TTTS; Twin-to-twin transfusion syndrome; Fetofetal transfusion syndrome; Fetal transfusion syndrome Twin to twin transfusion syndrome (TTTS) is a rare condition that occurs during a twin pregnancy when blood moves from one twin (the “donor twin”) to the other (the “recipient twin”) while in the womb. TTTS is a complication that specifically occurs in identical (monozygotic) twin pregnancies that share the same "egg" sac (monochorionic) that may or may not share the same amniotic sac (monoamniotic). TTTS usually develops between 15 and 26 weeks of pregnancy.

Illustration of a Fetoscopy and laser ablation of connecting vessels in Twin-to-twin transfusion syndrome

Cause

As a result of sharing a single placenta, the blood supplies of monochorionic twin fetuses can become connected, so that they share blood circulation: although each fetus uses its own portion of the placenta, the connecting blood vessels within the placenta allow blood to pass from one twin to the other. It is thought that most monochorionic placentae have these "shared connections" that cross the placenta, with the net flow volumes being equal between them.This state is sometimes referred to as "flow balance". When the placenta has deep vein-artery connection this can cause blood flow to become unbalanced. Depending on the number, type and direction of the interconnecting blood vessels (anastomoses), blood can be transferred disproportionately from one twin (the "donor") to the other (the "recipient"), due to a state of "flow imbalance" imparted by new blood vessel growth across the placental "equator", the line that divides each baby's proportion of the shared placenta. This state of transfusion causes the donor twin to have decreased blood volume, retarding the donor's development and growth, and also decreased urinary output, leading to a lower than normal level of amniotic fluid (becoming oligohydramnios). The blood volume of the recipient twin is increased, which can strain the fetus's heart and eventually lead to heart failure, and also higher than normal urinary output, which can lead to excess amniotic fluid (becoming polyhydramnios). The demise of the fetus is typically a result of ischemia related to the lack of blood flow. The lack of blood flow causes bowel atresia, brain damage, and kidney failure.

Symptoms

Most of the time, the donor twin is smaller than the other twin at birth. The infant often has anemia, is dehydrated, and looks pale. The recipient twin is born larger, with redness to the skin, too much blood, and a higher blood pressure. The twin that gets too much blood may develop cardiac failure because of the high blood volume. The infant may also need medicine to strengthen heart function. The unequal size of identical twins is referred to as discordant twins.

Diagnosis

This condition is most often diagnosed by ultrasound during pregnancy. After birth, the infants will receive the following tests:

• Blood clotting studies, including prothrombin time (PT) and partial thromboplastin time (PTT)
• Comprehensive metabolic panel to determine electrolyte balance
• Complete blood count
• Chest x-ray

Treatment

Treatment may require repeated amniocentesis during pregnancy. Fetal laser surgery may be done to stop the flow of blood from one twin to the other during pregnancy. After birth, treatment depends on the infant's symptoms. The donor twin may need a blood transfusion to treat anemia. The recipient twin may need to have the volume of body fluid reduced. This may involve an exchange transfusion. The recipient twin may also need to take medicine to prevent heart failure.

Prognosis

If the twin-to-twin transfusion is mild, both babies often recover fully. Severe cases may result in the death of a twin.

NIH genetic and rare disease info

• NIH info on Twin to twin transfusion syndrome

Twin to twin transfusion syndrome is a rare disease.

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