Twin-to-Twin Transfusion Syndrome

INTRODUCTION

Background: Twin-to-twin transfusion syndrome (TTTS) is the result of an intrauterine blood transfusion from one twin to another twin. TTTS occurs in monochorionic, monozygotic twins. The donor twin often is smaller and anemic at birth. The recipient twin usually is larger and plethoric at birth.

Pathophysiology: TTTS is the result of transfusion of blood from one fetal twin to another twin. The blood transfusion from the donor twin to the recipient twin occurs through placental vascular anastomoses. The most common vascular anastomosis is a deep, artery-to-vein anastomosis through a shared placental cotyledon. TTTS is a specific complication of monochorionic twin pregnancies. A uniform nomenclature describing the spectrum of TTTS does not exist.

One classification scheme separates TTTS into severe, moderate, and mild. Severe TTTS presents early in the second trimester at 16-18 weeks' gestation. A difference exists in fetal size of twins who are more than 1.5 weeks gestation. Umbilical cord sizes differ between the twins. Hemoglobin concentrations usually are the same in both twins because the transfusion is a whole blood shift. Polyhydramnios develops in the sac of the recipient twin because of volume overload and increased fetal urine output. Oligohydramnios develops in the sac of the donor twin because of hypovolemia and decreased urine output. Severe oligohydramnios can result in the stuck twin phenomena in which the twin appears in a fixed position against the uterine wall.

Moderate TTTS develops later in the second trimester between 24-30 weeks gestation. Although a fetal size discrepancy exists at more than 1.5 weeks gestation, polyhydramnios and oligohydramnios do not develop. The donor twin becomes anemic, hypovolemic, and growth is retarded. The recipient twin becomes plethoric, hypervolemic, and macrosomic. Either twin can develop hydrops fetalis. The donor twin can become hydropic because of anemia and high-output heart failure. The recipient twin can become hydropic because of hypervolemia. The recipient twin also can develop hypertension, hypertrophic cardiomegaly, disseminated intravascular coagulation, and hyperbilirubinemia after birth.

Mild TTTS develops slowly in the third trimester. Polyhydramnios and oligohydramnios usually do not develop. Hemoglobin concentrations differ by more than 5 g/dL. Twin size differs by more than 20%. Acute TTTS can occur at birth during the time between clamping the umbilical cords of the first and second twin. During this interval, the second twin has sole connection to the placenta and may receive a significant transfusion of blood.

Frequency:
　

• In the US: Monozygotic twins occur in 3-5 per1000 pregnancies. Monozygotic twins can be monochorionic or dichorionic. Approximately 75% of monozygotic twins are monochorionic. Only monochorionic twins are at risk for TTTS. TTTS occurs in 5-38% of monochorionic twins.

CLINICAL

History:

• Women with twin pregnancies who develop TTTS frequently complain of a rapidly enlarging abdomen over 2-3 weeks as polyhydramnios develops.

• Other complaints include preterm labor and premature rupture of membranes.

Physical: TTTS can be suspected in pregnant women carrying twins if they develop a rapidly increasing fundal height. After birth, TTTS can be suspected if significant differences in the appearance of monozygotic twins exist.

• Donor twin

• Small for gestational age - More than 20% smaller than recipient twin

• Pallor

• Poor peripheral perfusion

• Recipient twin

• Large for gestational age - More than 20% larger than donor twin

• Plethoric and ruddy

• Jaundice

• Hydrops fetalis can be present in either twin in TTTS. Infant has subcutaneous edema, distended abdomen, and respiratory distress.

DIFFERENTIALS

Other Problems to be Considered:

Hydrops Fetalis
Polycythemia
Polycythemia of the Newborn
Polyhydramnios and Oligohydramnios
Anemia of the newborn

WORKUP

Lab Studies:
　

• CBC: Donor twin frequently is anemic at birth. Recipient twin frequently is polycythemic at birth.

• Calcium: Hypocalcemia frequently is present in the donor twin.

• Glucose: Hypoglycemia may be present in either twin.

• Creatinine: Either twin may have evidence of renal dysfunction.

• Platelet count: Thrombocytopenia can occur in either twin.

• Bilirubin: Hyperbilirubinemia may develop in polycythemic recipient twin.

Imaging Studies:
　

• Head ultrasound: Premature twins are susceptible to intraventricular hemorrhage and periventricular leukomalacia.

• Echocardiogram: Myocardial dysfunction, myocardial hypertrophy, valvular insufficiency, and pericardial effusions can be detected in either twin.

• Renal ultrasound: Abnormal renal echogenicity may be present in either twin and indicate hypoxic-ischemic cortical necrosis.

• Abdominal ultrasound: Ascites may be present if hydrops fetalis occurs.

• Chest x-ray: Pleural effusions and cardiomegaly may be present if hydrops fetalis occurs.

TREATMENT

Medical Care: Detailed description of medical care of the pregnant woman carrying twins with TTTS is beyond the scope of this review. Medical care of twins after birth is directed toward problems related to prematurity, anemia, polycythemia, and hydrops fetalis.

• Severely anemic donor twins may require packed RBC transfusions or partial exchange transfusions.

• Polycythemic recipient twins may require partial exchange transfusion to lower serum hematocrits.

• Newborns with hydrops fetalis may require mechanical ventilation, thoracocentesis, pericardiocentesis, and paracentesis.

FOLLOW-UP

Complications:
　

• Neurologic sequelae: Intrauterine demise of one twin can result in neurologic sequelae in the surviving twin. Acute exsanguination of the surviving twin into the relaxed circulation of the deceased twin can result in intrauterine CNS ischemia.

Prognosis:
　

• Outcome is dependent upon gestational age at birth. The lower the gestational age at birth the greater the risk for long-standing neurologic or pulmonary sequelae. Catch-up growth occurs postnatally in most of the smaller donor twins.

MISCELLANEOUS

Medical/Legal Pitfalls:
　

• Monochorionic twin pregnancies are considered high-risk situations and require very close obstetrical monitoring. Newborns with TTTS may be critically ill at birth and require specialized care in neonatal intensive care units. These infants are at significant risk for neurologic sequelae.