Prevalence:

• 2-3% of monochorionic twins.

Ultrasound diagnosis:

• Monochorionic twins with one normal fetus (pump twin) and another with no cardiac acitivity (rarely, a rudimentary heart may show slow pulsations) and variable degrees of deficient development of the head and upper limbs and hydrops (recipient twin).
• Color Doppler in the recipient twin demonstrates reversed pulsatile flow from an umbilical arterioarterial anastomosis and venous return to the pump twin via a venovenous anastomosis. Occasionally, the cord of the acardiac twin arises directly from that of the pump twin.
• The size of the acardiac mass is prognostic value for the survival of the pump twin.
• About 50% of pump twins die before or after birth from congestive heart failure or severe preterm birth, due to polyhydramnios.

Associated abnormalities:

• The incidence of chromosomal abnormalities, genetic syndromes or fetal defects is not increased.

Investigations:

• Detailed ultrasound examination, including echocardiography to assess cardiac function in the pump twin.

Fetal therapy:

• Prenatal treatment is by occlusion of the blood flow to the acardiac twin. Several methods have been used, including ablation of umbilical cord vessels by laser or diathermy, coagulation of placental anastomoses by laser, or ablation of intrafetal vessels by monopolar diathermy, laser, or radiofrequency. When these methods are used at 16-18 weeks’ gestation the survival rate of the pump twin is about 80%.
• The preferred management is ultrasound-guided laser coagulation or radiofrequency of the umbilical cord vessels within the abdomen of the acardiac twin at 11-13 weeks. The survival is 70-75%, which is less than the 80% achieved with intervention at 16-18 weeks.
• However, delay in intervention between the diagnosis of TRAP sequence at 11-13 weeks’ gestation until 16-18 weeks is associated with spontaneous cessation of flow in the acardiac twin in 60% of cases and in about 50% of these there is also death or brain damage in the pump twin.

Follow up:

• Intrauterine intervention: scan in 1 week to confirm that the pump twin is alive and that there is cessation of flow in the acardiac twin. Subsequently, standard follow-up.
• No intrauterine intervention: scans every 2-3 weeks to monitor growth of the acardiac twin, heart function of the pump twin and amniotic fluid volume.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Depends on gestational age at birth.

Recurrence:

• No increased risk of recurrence.